Javascript switch with string variable not working

Question

Could anyone tell me why the below switch is not working?

var String=new String('String #1');

document.write(String);

document.write(' Check ');

switch(String)
{

    case 'String #1' : 
    document.write('String Number 1');
    break;
    default: document.write('wrong string');
}

The output is: String #1 Check wrong string

^ that, you should be getting `String is not a constructor` error — adeneo, Sep 22 '16 at 16:35
a) Don't create `String` instances b) don't overwrite `String` c) don't `switch` on `String` objects — Bergi, Sep 22 '16 at 16:37
When I name it differently, e.g. MyString, the same still happens. — Emile, Sep 22 '16 at 16:37
No errors when running this, just the output from the default statement. — Emile, Sep 22 '16 at 16:39
If you wrote `var String = 'String #1';` it should work with no problems. — , Sep 22 '16 at 16:41
`new String('String #1') !== 'String #1'`. First is an object, second a primitive value. And yes, switch uses strict comparison. — raina77ow, Sep 22 '16 at 16:42

score 3 · Answer 1 · edited May 23 '17 at 12:06

String is a constructor that's builtin to JavaScript. Naming variables that shadow these constructors will cause an error:

TypeError: String is not a constructor

Rename the String variable and do not use the switch statement here because you have a String instance. switch statements use strict comparison (===) per the MDN documentation and the ECMAScript 2015 specification. Since a string instance and literal are never 'strictly equal', comparison fails. Don't instantiate, instead use a literal:

var string = "String #1";

switch(string) {
  case "String #1":
    document.write("String Number 1");
    break;
  default: 
    document.write("wrong string");
}

Also, I don't recommend using document.write, see here. Logging or inserting into the DOM with createElement and appendChild should work sufficiently here.

Thank you all for advising, This works: If you wrote var String = 'String #1'; it should work with no problems. – torazaburo 56 mins ago I will check the other options as well. — Emile, Sep 22 '16 at 17:45

score 3 · Accepted Answer · answered Sep 22 '16 at 16:42

3

You must compare an Object with an Object not a String with an Object. Here I compare an object with an Object :

var string = "String #1";
console.log(string);
console.log("Check");

switch(string)
{
    case "String #1":
    console.log("String Number 1");
    break;
    default: console.log("wrong string");
}

answered Sep 22 '16 at 16:42

kevin ternet

3,779
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3

Correction "here you are comparing a string to a string" :) – Adam Buchanan Smith Sep 22 '16 at 18:11

score 1 · Answer 3 · answered Sep 22 '16 at 16:45

You can change the object to a string using toString() See example https://jsfiddle.net/DIRTY_SMITH/59x9xn3g/1/

<script>
var someObject =new String('String #1');
var someString = someObject.toString();
document.write(someString);

document.write(' Check ');

switch(someString)
{

    case 'String #1' : document.write('String Number 1');
    break;
    default: document.write('wrong string');
}
</script>

Javascript switch with string variable not working

3 Answers3