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Defining JavaScript functions, the ES6 way
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functions.html
<!DOCTYPE html>
<meta charset=utf-8 />
<title>Defining JavaScript functions, the ES6 way</title>
<h1>Defining JavaScript functions, the ES6 way</h1>
<em>Use Firefox 22 (Firefox Nightly)</em>
<script>
// old school
var square = function(x) {
return x * x;
}
console.log(square(3));
// Expression closures
// doc: http://mzl.la/10TNpzc
// *Edit:* I've been told that Expression Closures are not part of ES6. Still cool.
var square = function(x) x * x;
console.log(square(3));
// Arrow functions
// spec: http://bit.ly/KN3z1c
var square = x => { return x * x; };
console.log(square(3));
// Arrow function + expression closure
var square = x => x * x;
console.log(square(3));
// Destructuring assignment
// doc: http://mzl.la/Xed4Ua
var squareAndCube = x => [x*x, x*x*x];
var [s,c] = squareAndCube(3);
console.log(s + ", " + c);
</script>
@CamiloMM
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CamiloMM commented Sep 3, 2016 •
edited

@boban984: I was curious about your statements so I went and checked (Chrome v52). Let's see:

let wrapper = {
    method1: function() { return this },
    method2() { return this },
    method3: () => this,
    method4: function() { return (() => this)() },
    method5: function() { return (() => this) },
    method6: () => (() => this)(),
    method7: () => (() => this),
}

// all the following are true
wrapper.method1() === wrapper
wrapper.method2() === wrapper
wrapper.method3() === window
wrapper.method4() === wrapper
wrapper.method5()() === wrapper
wrapper.method6() === window
wrapper.method7()() === window

// of particular interest:
let wm4 = wrapper.method4.bind('wow')
let wm5 = wrapper.method5.bind('nice')
`${wm4()} ${wm5()()}` === 'wow nice'

I'm not sure why it acts like this, I thought this would always be window in an arrow function.

I also think arrow functions don't have constructors.

You don't need those, because you have classes now. I'm not sure everyone was fond of prototypal inheritance (though personally I liked it).

Moreover, you can always use traditional functional notation when you want the way it behaves. This new fat arrow notation makes Javascript more productive for functional programming (and brings it closer to languages like Haskell, while also having OOP features), and anyone who thinks it's not readable might want to stick to mantaining WordPress blog-sites and using drag-and-drop GUIs with big buttons.

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