有人可以向我解释函数中的一行代码吗

Question

Could someone please explain me what does this line of code actually means step by step.

arrRes.push(fn(arr[i]));

I understand the push part but I am struggling to grasp the code in the parenthesis.

The whole function looks like this :

function arrayCalc (arr, fn) {

    arrRes = [];

    for (let i = 0; i < arr.length; i++) {

        arrRes.push(fn(arr[i])); // <--- this line here in the parenthesis

    }
    return arrRes;
};

Sorry if this is a dumb question but I've watched the tutorial video for five times and I just can't understand what that line exactly means.

Thanks!

Answer 1

there is some function fn passed as argument and array arr

arrRes.push(fn(arr[i])); - means:

1. take value from arr (index is i )
2. execute function fn with value as a parameter
3. whatever is result, push it to arrRes

example

 function arrayCalc (arr, fn) { arrRes = []; for (let i = 0; i < arr.length; i++) { arrRes.push(fn(arr[i])); } return arrRes; }; const someArr = [1,2,3]; function someFunction(number) { return number * 10; } function someOtherFunction(number) { return `${number}_Z`; } console.log(arrayCalc(someArr, someFunction)) // [10, 20, 30] console.log(arrayCalc(someArr, someOtherFunction)) // ['1_Z', '2_Z', '3_Z']

Answer 2

This is usually called a mapping: apply a function to each element of a collection... Thus if you have an array [1,2,3] and map it with a function that multiplies a number by 2, you will end with an array equals to [2,4,6].

To compute it, you need an array, arr and a function fn . Then for each element of arr in turn you apply fn to it and place the result at the end of the new collection. You can write it as:

arrRes = [];
for (let i = 0; i < arr.length; i++) {
    var dummy = arr[i]; 
    var mapped = fn(dummy);
    arrRes.push(mapped);
}