Let’s try to illustrate the motivation and utility of this:
function identify() {
return this.name.toUpperCase();
}
function speak() {
var greeting = "Hello, I'm " + identify.call( this );
console.log( greeting );
}
var me = {
name: "Kyle"
};
var you = {
name: "Reader"
};
identify.call( me ); // KYLE
identify.call( you ); // READER
speak.call( me ); // Hello, I'm KYLE
speak.call( you ); // Hello, I'm READER
If the how of this snippet confuses you, don’t worry! We’ll get to that
shortly. Just set those questions aside briefly so we can look into the
why more clearly.
This code snippet allows the identify() and speak() functions to be
reused against multiple context objects (me and you), rather than need‐
ing a separate version of the function for each object.
Instead of relying on this, you could have explicitly passed in a context
object to both identify() and speak():
function identify(context) {
return context.name.toUpperCase();
}
function speak(context) {
var greeting = "Hello, I'm " + identify( context );
console.log( greeting );
}
identify( you ); // READER
speak( me ); // Hello, I'm KYLE
2 | Chapter 1: this or That?
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