I'm new to Javascript, just a question on 'this' when using anonymous function expression.
const testFunction = function () {
this.xxx = xxx;
};
later I call it as:
testFunction()
and there will be an error, because we can't use 'this' in this case,
but isn't that 'this' refer to the window object?
If your JavaScript is running in a web browser, under default circumstances, then this will be the window object.
const testFunction = function() {
console.log(this === window);
};
testFunction();If strict mode is enabled, then it will not.
Not only is automatic boxing a performance cost, but exposing the global object in browsers is a security hazard because the global object provides access to functionality that "secure" JavaScript environments must restrict. Thus for a strict mode function, the specified this is not boxed into an object, and if unspecified, this will be undefined:
"use strict";
const testFunction = function() {
console.log(this === window);
};
testFunction();