如何在普通 function 中写箭头 function

Question

Yes i saw a lot of suggestions about similar topic and most of them didn't solve my question

here is a code from a book am trying to understand the work of the arrow function as am very used to the normal function... how can i write the below code with a normal function..

thank you

const schools = ["Yorktown", "Washington & Liberty", "Wakefield"];
const wSchools = schools.filter(school => school[0] === "W");
console.log(wSchools);
// ["Washington & Liberty", "Wakefield"]

i have tried in this way but not getting the result i want

const wSchools = schools.filter(function(school) {
school[0] === "W";
return school;
});

thank you in advance for a thorough explanation.

Answer 1

Its super simple just change this

const wSchools = schools.filter(function(school) {
   school[0] === "W";
   return school;
});

To This

const wSchools = schools.filter(function(school) {
   return school[0] === "W";
});

Explanation: This is the basic syntax of Arrow function according to MDN

param => expression 

which can also be written as

(param) => { return expression }

Answer 2

You wrote the function correctly in terms of code correctness, but you have a logical error. You have to return a true or false when using an array filter.

const wSchools = schools.filter(function(school) {
return school[0] === "W";
});

Answer 3

Question has been answered, but the OP asked for understanding arrow functions, so let's go further now:

Arrow functions are simply functions that capture the scope of the current code block. It's super useful and I definitely encourage you to dig deeper in your understanding of these.

The particular form you encountered is the concise form where the body of the function can be reduced to a single return statement .

Take this regular function:

function(a, b) { return a === b }

It could be converted to this arrow function:

(a, b) => { return a === b }

But since our function only returns the result of a very simple test, we can make it shorter by straight out omitting both the curly braces and the return statement:

(a, b) => a === b

Nice and short, perfect for callbacks.

Here is some literature about arrow functions , hope you'll understand them better and get more comfortable using them, it will give you super powers:)