This question already has answers here:
Are 'Arrow Functions' and 'Functions' equivalent / interchangeable?
(4 answers)
Closed 4 years ago.
I prefer do function declaration
doSomething() //still works
function doSomething() {}
over
var doSomething = function() = {}
doSomething()
because with the function declaration, I don't have to worry about the order, it just got hoisted at the top. Now when it come to es6, my coworker like to do const doSomething = () => {} because for them they dislike the word 'function'. I lost the hoisting how can I fix it?
I hope I can do this
abc()
abc() => {}
but I have to use babel so that the word function can be ignore to make a function in es6/es7?
No you can't:
abc();
abc() => {console.log('test');}
Moreover, arrow functions do now have their own this context and cannot be used as constructors. Which means they are not only for people who do not want to use the function keyword.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions
Related
This question already has answers here:
Are 'Arrow Functions' and 'Functions' equivalent / interchangeable?
(4 answers)
What is the difference between "let" and "var"?
(39 answers)
Closed 3 months ago.
I want to be able to define a function (either regular or arrow) globally in the js window like this:
function myRegularFunction(){
console.log("hello from the regular function");
}
const myArrowFunction = () => {
console.log("hello from the arrow function");
}
and then be able to invoke it elsewhere like this:
window['myRegularFunction']();
window['myArrowFunction']();
When I define functions as stated above, I am then able to inovke the regular function, but the arrow funcion is not appearing in the js window, and thus I cannot invoke it.
From the console, I get:
window['myArrowFunction']
undefined
Can anyone help me with this issue?
This question already has answers here:
Are 'Arrow Functions' and 'Functions' equivalent / interchangeable?
(4 answers)
Closed 3 years ago.
I have a test function:
function test(element) {
console.log(element.id);
console.log(element);
}
which I want to use as a callback when my button <button id="testbtn">afsdasd</button> is pressed. If I do this:
document.getElementById('testbtn').onclick = () => {
test(this);
};
I get the following output:
However, if I do this:
document.getElementById('testbtn').onclick = function() {
test(this);
};
the output is different:
Why? I thought both versions were exactly the same?
The first one is an arrow function while the second one is a regular function. Arrow functions do not have their own this binding, so they will search this in the next outer lexical scope. In your case the enclosing lexical scope for the arrow function is the Window object.
An arrow function does not have its own this. The this value of the
enclosing lexical scope is used; arrow functions follow the normal
variable lookup rules. So while searching for this which is not
present in current scope, an arrow function ends up finding the this
from its enclosing scope. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions
This question already has answers here:
Methods in ES6 objects: using arrow functions
(6 answers)
Are 'Arrow Functions' and 'Functions' equivalent / interchangeable?
(4 answers)
Closed 4 years ago.
i have this object literal
let p = {
name : 'Amir',
say: () => {
console.log(this.name)
console.log(this)
}
}
and I want the say function works using this
p.say();
but the arrow function obviously gets the window object as 'this'. I know I could use a regular function for 'say' instead of arrow and it will work fine.
BUT
I would like to ONLY change the call to say function to make it work, but the binding won't work.
I mean something like p.say.bind(p)() or p.say.call(p) aint gonna work as desired.
Is it possible to change the call to function ONLY and not the say function?
This question already has answers here:
Are 'Arrow Functions' and 'Functions' equivalent / interchangeable?
(4 answers)
Methods in ES6 objects: using arrow functions
(6 answers)
Closed 4 years ago.
Can't find this info anywhere on the web. Is there any difference (e.g. in performance) between these two methods created with object literal syntax? Or is the mechanism under the hood exactly the same?
let test = {
foo(){
console.log("foo");
return 1;
},
bar: () => {
console.log("bar");
}
}
console.log(test.foo());
console.log(test.bar());
There shouldn't be any performance difference -- the shorthand function property is just syntactic sugar.
However, there's an operational difference. The shorthand notation is short for the traditional function syntax, not an arrow function. So it's equivalent to:
foo: function() {
console.log("foo");
}
Arrow functions have a number of different behaviors from traditional function expressions. See Arrow function vs function declaration / expressions: Are they equivalent / exchangeable?
Your example functions don't do anything that depends on the differences, but in a real application they might.
This question already has answers here:
Are 'Arrow Functions' and 'Functions' equivalent / interchangeable?
(4 answers)
Closed 5 years ago.
I have an arrow function that I am trying to execute with call(). For the sake of simplification, as follows:
Operational as expected
const func = (e) => {
console.log(e)
}
func.call(null, e)
Hmm ... what's going on here?
I would expect the following code to pass element into func as this.
const func = (e) => {
console.log(this)
console.log(e)
}
func.call(element, e)
But, instead this remains undefined.
If I switch it to a regular function definition, all works as expected.
const func = function (e) {
console.log(this)
console.log(e)
}
func.call(element, e)
Question
Why am I not able to pass a context for this into an arrow function from call()?
this is not bound in arrow functions, so call() and apply() can only pass in parameters. this is ignored
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions#Invoked_through_call_or_apply
In ES6 this has lexical scope meaning value of this inside arrow function would be same as that outside of arrow function. In pre-ES6 form this is the object that you passed as a first argument to call method.