What does the ...
do in this React (using JSX) code and what is it called?
<Modal {...this.props} title='Modal heading' animation={false}>
What does the ...
do in this React (using JSX) code and what is it called?
<Modal {...this.props} title='Modal heading' animation={false}>
That's property spread notation. It was added in ES2018 (spread for arrays/iterables was earlier, ES2015), but it's been supported in React projects for a long time via transpilation (as "JSX spread attributes" even though you could do it elsewhere, too, not just attributes).
{...this.props}
spreads out the "own" enumerable properties in props
as discrete properties on the Modal
element you're creating. For instance, if this.props
contained a: 1
and b: 2
, then
<Modal {...this.props} title='Modal heading' animation={false}>
would be the same as
<Modal a={this.props.a} b={this.props.b} title='Modal heading' animation={false}>
But it's dynamic, so whatever "own" properties are in props
are included.
Since children
is an "own" property in props
, spread will include it. So if the component where this appears had child elements, they'll be passed on to Modal
. Putting child elements between the opening tag and closing tags is just syntactic sugar — the good kind — for putting a children
property in the opening tag. Example:
class Example extends React.Component {
render() {
const { className, children } = this.props;
return (
<div className={className}>
{children}
</div>
);
}
}
ReactDOM.render(
[
<Example className="first">
<span>Child in first</span>
</Example>,
<Example className="second" children={<span>Child in second</span>} />
],
document.getElementById("root")
);
.first {
color: green;
}
.second {
color: blue;
}
<div id="root"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>
Spread notation is handy not only for that use case, but for creating a new object with most (or all) of the properties of an existing object — which comes up a lot when you're updating state, since you can't modify state directly:
this.setState(prevState => {
return {foo: {...prevState.foo, a: "updated"}};
});
That replaces this.state.foo
with a new object with all the same properties as foo
except the a
property, which becomes "updated"
:
const obj = {
foo: {
a: 1,
b: 2,
c: 3
}
};
console.log("original", obj.foo);
// Creates a NEW object and assigns it to `obj.foo`
obj.foo = {...obj.foo, a: "updated"};
console.log("updated", obj.foo);
.as-console-wrapper {
max-height: 100% !important;
}
...
are called spread attributes which, as the name represents, it allows an expression to be expanded.
var parts = ['two', 'three'];
var numbers = ['one', ...parts, 'four', 'five']; // ["one", "two", "three", "four", "five"]
And in this case (I'm going to simplify it).
// Just assume we have an object like this:
var person= {
name: 'Alex',
age: 35
}
This:
<Modal {...person} title='Modal heading' animation={false} />
is equal to
<Modal name={person.name} age={person.age} title='Modal heading' animation={false} />
So in short, it's a neat short-cut, we can say.
The three dots represent the spread operator in ES6. It allows us to do quite a few things in JavaScript:
Concatenate arrays
var shooterGames = ['Call of Duty', 'Far Cry', 'Resident Evil'];
var racingGames = ['Need For Speed', 'Gran Turismo', 'Burnout'];
var games = [...shooterGames, ...racingGames];
console.log(games) // ['Call of Duty', 'Far Cry', 'Resident Evil', 'Need For Speed', 'Gran Turismo', 'Burnout']
Destructuring an array
var shooterGames = ['Call of Duty', 'Far Cry', 'Resident Evil'];
var [first, ...remaining] = shooterGames;
console.log(first); //Call of Duty
console.log(remaining); //['Far Cry', 'Resident Evil']
Combining two objects
var myCrush = {
firstname: 'Selena',
middlename: 'Marie'
};
var lastname = 'my last name';
var myWife = {
...myCrush,
lastname
}
console.log(myWife); // {firstname: 'Selena',
// middlename: 'Marie',
// lastname: 'my last name'}
There's another use for the three dots which is known as Rest Parameters and it makes it possible to take all of the arguments to a function in as one array.
Function arguments as array
function fun1(...params) {
}
The three dots in JavaScript are the spread / rest operator.
Spread operator
The spread syntax allows an expression to be expanded in places where multiple arguments are expected.
myFunction(...iterableObj);
[...iterableObj, 4, 5, 6]
[...Array(10)]
Rest parameters
The rest parameter syntax is used for functions with a variable number of arguments.
function(a, b, ...theArgs) {
// ...
}
The spread / rest operator for arrays was introduced in ES6. There's a State 2 proposal for object spread / rest properties.
TypeScript also supports the spread syntax and can transpile that into older versions of ECMAScript with minor issues.
This is a feature of ES6, which is used in React as well. Look at the below example:
function Sum(x, y, z) {
return x + y + z;
}
console.log(Sum(1, 2, 3)); // 6
This way is fine if we have a maximum of three parameters. But, what if we need to add, for example, 110 parameters. Should we define them all and add them one by one?
Of course there is an easier way to do, which is called spread. Instead of passing all those parameters you write:
function (...numbers){}
We have no idea how many parameters we have, but we know there are heaps of those.
Based on ES6, we can rewrite the above function as below and use the spread and mapping between them to make it as easy as a piece of cake:
let Sum = (...numbers) => {
return numbers.reduce((prev, current) => prev + current);
}
console.log(Sum(1, 2, 3, 4, 5, 6, 7, 8, 9)); // 45
It's just defining props in a different way in JSX for you!
It's using ...
array and object operator in ES6 (object one not fully supported yet), so basically if you already define your props, you can pass it to your element this way.
So in your case, the code should be something like this:
function yourA() {
const props = {name='Alireza', age='35'};
<Modal {...props} title='Modal heading' animation={false} />
}
so the props you defined, now separated and can be reused if necessary.
It's equal to:
function yourA() {
<Modal name='Alireza' age='35' title='Modal heading' animation={false} />
}
These are the quotes from React team about spread operator in JSX:
JSX Spread Attributes If you know all the properties that you want to place on a component ahead of time, it is easy to use JSX:
var component = <Component foo={x} bar={y} />;
Mutating Props is Bad
If you don't know which properties you want to set, you might be tempted to add them onto the object later:
var component = <Component />;
component.props.foo = x; // bad
component.props.bar = y; // also bad
This is an anti-pattern because it means that we can't help you check the right propTypes until way later. This means that your propTypes errors end up with a cryptic stack trace.
The props should be considered immutable. Mutating the props object somewhere else could cause unexpected consequences so ideally it would be a frozen object at this point.
Spread Attributes
Now you can use a new feature of JSX called spread attributes:
var props = {};
props.foo = x;
props.bar = y;
var component = <Component {...props} />;
The properties of the object that you pass in are copied onto the component's props.
You can use this multiple times or combine it with other attributes. The specification order is important. Later attributes override previous ones.
var props = { foo: 'default' };
var component = <Component {...props} foo={'override'} />;
console.log(component.props.foo); // 'override'
What's with the weird ... notation?
The ... operator (or spread operator) is already supported for arrays in ES6. There is also an ECMAScript proposal for Object Rest and Spread Properties. We're taking advantage of these supported and developing standards in order to provide a cleaner syntax in JSX.
Kudos to Brandon Morelli. He explained perfectly here, but links may die so I am just pasting the content below:
The spread syntax is simply three dots: ...
It allows an iterable to expand in places where 0+ arguments are expected.
Definitions are tough without context. Let's explore some different use cases to help understand what this means.
Take a look at the code below. In this code, we don’t use the spread syntax:
var mid = [3, 4];
var arr = [1, 2, mid, 5, 6];
console.log(arr);
Above, we’ve created an array named mid
. We then create a second array which contains our mid
array. Finally, we log out the result. What do you expect arr
to print? Click run above to see what happens. Here is the output:
[1, 2, [3, 4], 5, 6]
Is that the result you expected?
By inserting the mid
array into the arr
array, we’ve ended up with an array within an array. That’s fine if that was the goal. But what if you want only a single array with the values of 1 through 6? To accomplish this, we can use the spread syntax! Remember, the spread syntax allows the elements of our array to expand.
Let’s look at the code below. Everything is the same — except we’re now using the spread syntax to insert the mid
array into the arr
array:
var mid = [3, 4];
var arr = [1, 2, ...mid, 5, 6];
console.log(arr);
And when you hit the run button, here’s the result:
[1, 2, 3, 4, 5, 6]
Awesome!
Remember the spread syntax definition you just read above? Here’s where it comes into play. As you can see, when we create the arr
array and use the spread operator on the mid
array, instead of just being inserted, the mid
array expands. This expansion means that each and every element in the mid
array is inserted into the arr
array. Instead of nested arrays, the result is a single array of numbers ranging from 1 to 6.
JavaScript has a built-in math object that allows us to do some fun math calculations. In this example we’ll be looking at Math.max()
. If you’re unfamiliar, Math.max()
returns the largest of zero or more numbers. Here are a few examples:
Math.max();
// -Infinity
Math.max(1, 2, 3);
// 3
Math.max(100, 3, 4);
// 100
As you can see, if you want to find the maximum value of multiple numbers, Math.max()
requires multiple parameters. You unfortunately can’t simply use a single array as input. Before the spread syntax, the easiest way to use Math.max()
on an array is to use .apply()
.
var arr = [2, 4, 8, 6, 0];
function max(arr) {
return Math.max.apply(null, arr);
}
console.log(max(arr));
It works, it’s just really annoying.
Now take a look at how we do the same exact thing with the spread syntax:
var arr = [2, 4, 8, 6, 0];
var max = Math.max(...arr);
console.log(max);
Instead of having to create a function and utilize the apply method to return the result of Math.max()
, we only need two lines of code! The spread syntax expands our array elements and inputs each element in our array individually into the Math.max()
method!
In JavaScript, you can’t just copy an array by setting a new variable equal to already existing array. Consider the following code example:
var arr = ['a', 'b', 'c'];
var arr2 = arr;
console.log(arr2);
When you press run, you’ll get the following output:
['a', 'b', 'c']
Now, at first glance, it looks like it worked — it looks like we’ve copied the values of arr into arr2. But that’s not what has happened. You see, when working with objects in JavaScript (arrays are a type of object) we assign by reference, not by value. This means that arr2 has been assigned to the same reference as arr. In other words, anything we do to arr2 will also affect the original arr array (and vice versa). Take a look below:
var arr = ['a', 'b', 'c'];
var arr2 = arr;
arr2.push('d');
console.log(arr);
Above, we’ve pushed a new element d into arr2. Yet, when we log out the value of arr, you’ll see that the d value was also added to that array:
['a', 'b', 'c', 'd']
No need to fear though! We can use the spread operator! Consider the code below. It’s almost the same as above. Instead though, we’ve used the spread operator within a pair of square brackets:
var arr = ['a', 'b', 'c'];
var arr2 = [...arr];
console.log(arr2);
Hit run, and you’ll see the expected output:
['a', 'b', 'c']
Above, the array values in arr expanded to become individual elements which were then assigned to arr2. We can now change the arr2 array as much as we’d like with no consequences on the original arr array:
var arr = ['a', 'b', 'c'];
var arr2 = [...arr];
arr2.push('d');
console.log(arr);
Again, the reason this works is because the value of arr is expanded to fill the brackets of our arr2 array definition. Thus, we are setting arr2 to equal the individual values of arr instead of the reference to arr like we did in the first example.
As a fun final example, you can use the spread syntax to convert a string into an array. Simply use the spread syntax within a pair of square brackets:
var str = "hello";
var chars = [...str];
console.log(chars);
For those who come from the Python world, JSX Spread Attributes are equivalent to
Unpacking Argument Lists (the Python **
-operator).
I'm aware this is a JSX question, but working with analogies sometimes helps to get it faster.
Three dots ...
represent spread operators or rest parameters.
It allows an array expression or string or anything which can be iterating to be expanded in places where zero or more arguments for function calls or elements for array are expected.
var arr1 = [1,2,3];
var arr2 = [4,5,6];
arr1 = [...arr1, ...arr2];
console.log(arr1); //[1, 2, 3, 4, 5, 6]
var arr = [1, 2, 3];
var arr2 = [...arr];
console.log(arr); //[1, 2, 3]
Note: Spread syntax effectively goes one level deep while copying an array. Therefore, it may be unsuitable for copying multidimensional arrays as the following example shows (it's the same with Object.assign() and spread syntax).
var arr1 = [4, 5]
var arr2 = [1, 2, 3, ...arr1, 6]
console.log(arr2); // [1, 2, 3, 4, 5, 6]
var dateFields = [1970, 0, 1]; // 1 Jan 1970
var d = new Date(...dateFields);
console.log(d);
var obj1 = { foo: 'bar', x: 42 };
var obj2 = { foo: 'baz', y: 13 };
var clonedObj = { ...obj1 };
console.log(clonedObj); // {foo: "bar", x: 42}
var mergedObj = { ...obj1, ...obj2 };
console.log(mergedObj); // {foo: "baz", x: 42, y: 13}
Note that the foo
property of obj1 has been overwritten by the obj2 foo
property.
function sum(...theArgs) {
return theArgs.reduce((previous, current) => {
return previous + current;
});
}
console.log(sum(1, 2, 3)); //6
console.log(sum(1, 2, 3, 4)); //10
Note: The spread syntax (other than in the case of spread properties) can be applied only to iterable objects:
So the following will throw an error:
var obj = {'key1': 'value1'};
var array = [...obj]; // TypeError: obj is not iterable
The ...
(spread operator) is used in React to:
provide a neat way to pass props from parent to child components. E.g., given these props in a parent component,
this.props = {
username: "danM",
email: "dan@mail.com"
}
they could be passed in the following manner to the child,
<ChildComponent {...this.props} />
which is similar to this
<ChildComponent username={this.props.username} email={this.props.email} />
but way cleaner.
...
(three dots in JavaScript) is called the Spread Syntax or Spread Operator. This allows an iterable such as an array expression or string to be expanded or an object expression to be expanded wherever placed. This is not specific to React. It is a JavaScript operator.
All these answers here are helpful, but I want to list down the mostly used practical Use Cases of the Spread Syntax (Spread Operator).
1. Combine Arrays (Concatenate Arrays)
There are a variety of ways to combine arrays, but the spread operator allows you to place this at any place in an array. If you'd like to combine two arrays and place elements at any point within the array, you can do as follows:
var arr1 = ['two', 'three'];
var arr2 = ['one', ...arr1, 'four', 'five'];
// arr2 = ["one", "two", "three", "four", "five"]
2. Copying Arrays
When we wanted a copy of an array, we used to have the Array.prototypr.slice() method. But, you can do the same with the spread operator.
var arr = [1,2,3];
var arr2 = [...arr];
// arr2 = [1,2,3]
3. Calling Functions without Apply
In ES5, to pass an array of two numbers to the doStuff()
function, you often use the Function.prototype.apply() method as follows:
function doStuff (x, y, z) { }
var args = [0, 1, 2];
// Call the function, passing args
doStuff.apply(null, args);
However, by using the spread operator, you can pass an array into the function.
doStuff(...args);
4. Destructuring Arrays
You can use destructuring and the rest operator together to extract the information into variables as you'd like them:
let { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
console.log(x); // 1
console.log(y); // 2
console.log(z); // { a: 3, b: 4 }
5. Function Arguments as Rest Parameters
ES6 also has the three dots ( ...) which is a rest parameter that collects all remaining arguments of a function into an array.
function f(a, b, ...args) {
console.log(args);
}
f(1,2,3,4,5);
// [ 3, 4, 5 ]
6. Using Math Functions
Any function where spread is used as the argument can be used by functions that can accept any number of arguments.
let numbers = [9, 4, 7, 1];
Math.min(...numbers); // 1
7. Combining Two Objects
You can use the spread operator to combine two objects. This is an easy and cleaner way to do it.
var carType = {
model: 'Toyota',
yom: '1995'
};
var carFuel = 'Petrol';
var carData = {
...carType,
carFuel
}
console.log(carData);
// {
// model: 'Toyota',
// yom: '1995',
// carFuel = 'Petrol'
// }
8. Separate a String into Separate Characters
You can use the spread operator to spread a string into separate characters.
let chars = ['A', ...'BC', 'D'];
console.log(chars); // ["A", "B", "C", "D"]
You can think of more ways to use the Spread Operator. What I have listed here are the popular use cases of it.
For someone who wants to understand this simple and fast:
First of all, this is not a syntax only to React. This is syntax from ES6 called spread syntax which iterate (merge, add, etc.) the array and object. Read more about it here.
So to answer the question:
Let's imagine you have this tag:
<UserTag name="Supun" age="66" gender="male" />
And you do this:
const user = {
"name"=>"Joe",
"age"=>"50"
"test"=>"test-val"
};
<UserTag name="Supun" gender="male" {...user} age="66" />
Then the tag will be equal to this:
<UserTag name="Joe" gender="male" test="test-val" age="66" />
So when you used the spread syntax in a React tag, it took the tag's attribute as object attributes which merge (replace if it exists) with the given object user
. Also, you might have noticed one thing that it only replaces before attribute, not after attributes. So in this example, age remains as it is.
The three dots (...)
are called the spread operator, and this is conceptually similar to the ES6 array spread operator, JSX
taking advantage of these supported and developing standards in order to provide a cleaner syntax in JSX
Spread properties in object initializers copies own enumerable properties from a provided object onto the newly created object.
let n = { x, y, ...z }; n; // { x: 1, y: 2, a: 3, b: 4 }
References:
Spread Attributes used to Pass the multiple Properties in a Simple Way
{ ... this.props } is Holding the property of this.props
Use of the { ... } Spread Operator with below props
this.props = { firstName: 'Dan', lastName: 'Abramov', city: 'New York', country: 'USA' }
Without { ... } Spread
<Child firstName={this.props.firstName} lastName={this.props.lastName} city={this.props.city} country={this.props.country} >
With { ... } Spread
<Child { ...this.props } />
Dan Abramov's Tweet about Spread operator (Creator of Redux)
These three dots are called the spread operator.
The spread operator helps us to create a copy state or props in React.
Using spread operator in React state
const [myState, setMyState] = useState({
variable1: 'test',
variable2: '',
variable3: ''
});
setMyState({...myState, variable2: 'new value here'});
In the above code, the spread operator will maintain a copy of the current state and we will also add a new value at the same time. If we don't do this, then the state will have only a value of variable2. The spread operator helps us to write optimized code.
In short, the three dots ...
is a spread operator in ES6 (ES2015). The spread operator will fetch all the data.
let a = [1, 2, 3, 4];
let b = [...a, 4, 5, 6];
let c = [7, 8, ...a];
console.log(b);
Will give the result [1, 2, 3, 4, 5, 6]
console.log(c);
Will give the result [7, 8, 1, 2, 3, 4]
The meaning of ... depends on where you use it in the code,
const numbers = [1,2,3];
const newNumbers = [...numbers, 4];
console.log(newNumbers) //prints [1,2,3,4]
const person = {
name: 'Max'
};
const newPerson = {...person, age:28};
console.log(newPerson); //prints {name:'Max', age:28}
const filter = (...args) => {
return args.filter(el => el ===1);
}
console.log(filter(1,2,3)); //prints [1]
This a spread operator...
For example, if you have an array first=[1,2,3,4,5]
and another second=[6,7,8]
.
[...first, ...second] // result is [1, 2, 3, 4, 5, 6, 7, 8]
The same can also be done with JSON objects.
It is usually called the spread operator. It is use to expand wherever is required.
Example:
const SomeStyle = {
margin: 10,
background: #somehexa
}
You can use this wherever you require it.
More about the spread operator: Spread syntax.
This syntax is part of ES6 and not something which you can use only in React. It can be used in two different ways; as a spread operator or as a rest parameter. You can find more from this article: ES6 Spread Operator in React by Example: Props and setState
What you have mentioned in the question is something like the following. Let's assume like this,
function HelloUser() {
return <Hello Name="ABC" City="XYZ" />;
}
With the use of spread operator you can pass props to the component like this:
function HelloUser() {
const props = {Name: 'ABC', City: 'XYZ'};
return <Hello {...props} />;
}
The spread operator is three dots (...) that performs several different tasks. First, the spread operator allows us to combine the contents of arrays.
var peaks = ["Tallac", "Ralston", "Rose"]
var canyons = ["Ward", "Blackwood"]
var tahoe = [...peaks, ...canyons]
console.log(tahoe.join(', ')) // Tallac, Ralston, Rose, Ward, Blackwood
The spread operator can also be used to get some, or the rest, of the items in the array:
var lakes = ["Donner", "Marlette", "Fallen Leaf", "Cascade"]
var [first, ...rest] = lakes
console.log(rest.join(", ")) // "Marlette, Fallen Leaf, Cascade"
We can also use the spread operator to collect function arguments as an array.
function directions(...args) {
var [start, ...remaining] = args
var [finish, ...stops] = remaining.reverse()
console.log(start, finish)
}
The spread operator can also be used for objects.
var morning = {
breakfast: "oatmeal",
lunch: "peanut butter and jelly"
}
var dinner = "mac and cheese"
var backpackingMeals = {
...morning,
dinner
}
console.log(backpackingMeals) // {breakfast: "oatmeal", lunch: "peanut butter and jelly", dinner: "mac and cheese"}
Ref: Learning React: Functional Web Development with React and Redux by Alex Banks and Eve Porcello
It is called spreads syntax in JavaScript.
It use for destructuring an array or object in JavaScript.
Example:
const objA = { a: 1, b: 2, c: 3 }
const objB = { ...objA, d: 1 }
/* Result of objB will be { a: 1, b: 2, c: 3, d: 1 } */
console.log(objB)
const objC = { ....objA, a: 3 }
/* result of objC will be { a: 3, b: 2, c: 3, d: 1 } */
console.log(objC)
You can do it same result with Object.assign()
function in JavaScript.
Reference: Spread syntax
It is common practice to pass props around in a React application. In doing this we able to apply state changes to the child component regardless of whether it is Pure or Impure (stateless or stateful). There are times when the best approach, when passing in props, is to pass in singular properties or an entire object of properties. With the support for arrays in ES6 we were given the "..." notation and with this we are now able to achieve passing an entire object to a child.
The typical process of passing props to a child is noted with this syntax:
var component = <Component foo={x} bar={y} />;
This is fine to use when the number of props is minimal but becomes unmanageable when the prop numbers get too much higher. A problem with this method occurs when you do not know the properties needed within a child component and the typical JavaScript method is to simple set those properties and bind to the object later. This causes issues with propType checking and cryptic stack trace errors that are not helpful and cause delays in debugging. The following is an example of this practice, and what not to do:
var component = <Component />;
component.props.foo = x; // bad
component.props.bar = y;
This same result can be achieved but with more appropriate success by doing this:
var props = {};
props.foo = x;
props.bar = y;
var component = Component(props); // Where did my JSX go?
But does not use JSX spread or JSX so to loop this back into the equation we can now do something like this:
var props = {};
props.foo = x;
props.bar = y;
var component = <Component {...props} />;
The properties included in "...props" are foo: x, bar: y. This can be combined with other attributes to override the properties of "...props" using this syntax:
var props = { foo: 'default' };
var component = <Component {...props} foo={'override'} />;
console.log(component.props.foo); // 'override'
In addition we can copy other property objects onto each other or combine them in this manner:
var oldObj = { foo: 'hello', bar: 'world' };
var newObj = { ...oldObj, foo: 'hi' };
console.log(newObj.foo); // 'hi';
console.log(newObj.bar); // 'world';
Or merge two different objects like this (this is not yet available in all react versions):
var ab = { ...a, ...b }; // merge(a, b)
Another way of explaining this, according to Facebook's react/docs site is:
If you already have "props" as an object, and you want to pass it in JSX, you can use "..." as a SPREAD operator to pass the whole props object. The following two examples are equivalent:
function App1() {
return <Greeting firstName="Ben" lastName="Hector" />;
}
function App2() {
const props = {firstName: 'Ben', lastName: 'Hector'};
return <Greeting {...props} />;
}
Spread attributes can be useful when you are building generic containers. However, they can also make your code messy by making it easy to pass a lot of irrelevant props to components that don't care about them. This syntax should be used sparingly.
It’s the called spread operator.
For example,
let hello={name: '',msg:''}
let hello1={...hello}
Now the hello
object properties are copied to hello1
.
This will be compiled into:
React.createElement(Modal, { ...this.props, title: "Modal heading", animation: false }, child0, child1, child2, ...)
where it gives two more properties, title
and animation
, beyond the props
the host element has.
...
is the ES6 operator called spread.
See Spread syntax
The spread operator (triple operator) introduced in ECMAScript 6 (ES6). ECMAScript (ES6) is a wrapper of JavaScript.
The spread operator enumerable properties in props.
this.props = { firstName: 'Dan', lastName: 'Abramov', city: 'New York', country: 'USA' } <Modal {...this.props} title='Modal heading' animation={false}>
{...this.props} = { firstName: 'Dan', lastName: 'Abramov', city: 'New York', country: 'USA' }
But the main feature spread operator is used for a reference type.
For example,
let person= {
name: 'Alex',
age: 35
}
person1 = person;
person1.name = "Raheel";
console.log( person.name); // Output: Raheel
This is called a reference type. One object affects other objects, because they are shareable in memory. If you are getting a value independently means spread memory and both use the spread operator.
let person= {
name: 'Alex',
age: 35
}
person2 = {...person};
person2.name = "Shahzad";
console.log(person.name); // Output: Alex
if you have an array of elements and you want to display the elements you just use ...arrayemaments and it will iterate over all the elements
//Try this way using spread syntax example
"The Math object of Javascript doesn't take in a single array as an argument but with
the spread syntax, the array is expanded into a number of arguments"
//Passing elements of the array as arguments to the Math Object
const arr = [1,2,500,-1,.20,0,-10];
console.log(Math.min(...arr));
console.log(Math.max(...arr));
This is a new feature in ES6/Harmony. It is called the spread operator.
It lets you either separate the constituent parts of an array/object, or take multiple items/parameters and glue them together. Here is an example:
let array = [1,2,3]
let array2 = [...array]
// array2 is now filled with the items from array
And with an object/keys:
// Let’s pass an object as props to a react component
let myParameters = {myKey: 5, myOtherKey: 7}
let component = <MyComponent {...myParameters}/>
// This is equal to <MyComponent myKey=5 myOtherKey=7 />
What's really cool is you can use it to mean "the rest of the values".
const myFunc = (value1, value2, ...values) {
// Some code
}
myFunc(1, 2, 3, 4, 5)
// When myFunc is called, the rest of the variables are placed into the "values" array
Those are called spreads. Just as the name implies, it means it's putting whatever the value of it in those array or objects.
Such as:
let a = [1, 2, 3];
let b = [...a, 4, 5, 6];
console.log(b);
> [1, 2, 3, 4, 5, 6]