Question 186175 in Javascript Question posted in
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Javascript – What's the meaning of "=>" when not calling a function?

I’m learning JavaScript through freeCodeCamp and the way they explained (or rather, didn’t) arrow functions has led to some massive confusion for me.

I am familiar with calling a function using arrow notation like this:

const myFunc = () => "value";

But in one of the later challenges, the code they provided calls a function I have to write using the following code:

findElement([1, 2, 3, 4], num => num % 2 === 0);

Here, the arrow notation is used as a parameter for a function, and not when calling a function. I have no idea what it means.

I managed to write a function that works:

function findElement(arr, func) {
  let num;
  for(let i = 0; i < arr.length; i++){
    num = arr[i];
    console.log(num);
    if (func(num)) {
      return num; 
    } 
  }
}

but I don’t understand why it works

Tags:

3

Answers


  1. 0

    I believe it means equal to or greater than.

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  2. 0

    => is the arrow function expressions.

    It is a compact alternative to a traditional function expression.

    You can find out more on https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions.

    For example, the following function definition:

    let f = function(arg1, arg2, ...) {
  return true;
};

    can be shortened with the =>:

    let f = (arg1, arg2, ...) => true;
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  3. 0

    As stated => is an arrow function – a shorter version of writing a normal function, but with some gotchas.

    In your following code, the () is necessary because the function is taking no parameters…

    const myFunc = () => "value";
console.log(myFunc()); // Results in "value"

    If you had one parameter, then you can lose the brackets (although you don’t have to)… both the following are both valid…

    const myFunc = myArg => "value " + myArg;
const myFunc = (myArg) => "value " + myArg;
console.log(myFunc("a")); // Result in "value a";

    If you had two or more parameters, then you also need the brackets…

    const myFunc = (myArg1, myArg2) => "value";
const myFunc = (myArg1, myArg2, myArg3) => "value";

    As a result in the following code, you are creating an arrow function with a single parameter (num) and so it doesn’t need the brackets (these are identical)…

    findElement([1, 2, 3, 4], num => num % 2 === 0);
findElement([1, 2, 3, 4], (num) => num % 2 === 0);

    The gotchas I mentioned earlier are to do with binding to keywords like this, arguments and super… which you can read more about in the documentation

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