84 lines
2.1 KiB
Markdown
84 lines
2.1 KiB
Markdown
---
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title: Arrow Functions
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---
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Arrow functions are a new ES6 syntax for writing JavaScript function expressions. The shorter syntax saves time, as well as simplifying the function scope.
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## What are arrow functions?
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An arrow function expression is a more concise syntax for writing function expressions using a "fat arrow" token (`=>`).
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### The basic syntax
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Below is a basic example of an arrow function:
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```javascript
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// ES5 syntax
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var multiply = function(x, y) {
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return x * y;
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};
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// ES6 arrow function
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var multiply = (x, y) => { return x * y; };
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// Or even simpler
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var multiply = (x, y) => x * y;
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```
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You no longer need the `function` and `return` keywords, or even the curly brackets.
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```javascript
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// everything included
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const multiply = function(x, y) => { return x * y };
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// remove "function"
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const multiply = (x, y) => { return x * y };
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// remove curly brackets and "return" ==> this way it returns implicitly
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const multiply = (x, y) => x * y;
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// if you only have one argument/parameter
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const multiplyBy2 = x => x * 2;
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// combined with the ternary operator, but note it's not a looker!
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const addOrMultiply = (x, y, mathOperator) => mathOperator.toLowerCase() === 'add' ? x + y : x * y;
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```
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### A simplified `this`
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Before arrow functions, new functions defined their own `this` value. To use `this` inside a traditional function expression, we have to write a workaround like so:
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```javascript
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// ES5 syntax
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function Person() {
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// we assign `this` to `self` so we can use it later
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var self = this;
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self.age = 0;
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setInterval(function growUp() {
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// `self` refers to the expected object
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self.age++;
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}, 1000);
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}
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```
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An arrow function doesn't define it's own `this` value, it inherits `this` from the enclosing function:
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```javascript
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// ES6 syntax
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function Person(){
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this.age = 0;
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setInterval(() => {
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// `this` now refers to the Person object, brilliant!
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this.age++;
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}, 1000);
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}
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var p = new Person();
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```
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#### Further Reading
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<a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions' target='_blank' rel='nofollow'>MDN link</a>
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