weird part 52 — map function, underscore.js

#vanila

var arr1 = [1,2,3];
function mapForEach(arr, fn){
    var newArr = [];
    for(var i = 0; i < arr.length; i++){
        newArr.push(
            fn(arr[i])//1,2,3 - value
        )
    }
    return newArr;
}
var arr2 = mapForEach(arr1, function(value){
    return value * 3;
});
console.log(arr2)
//vanila 
var arr3 = arr1.map(item => item * 3)
console.log(arr3)

#es5

array.map(function(currentValue, index{
 
  //your code
}

#underscore.js

https://underscorejs.org/#map

//underscore
var arr4 = _.map(arr1, item => item * 3)
console.log(arr4)