Javascript Ruby's map-like method

Question

Is there Ruby's map-like syntax in JavaScript ? for example in Ruby I could write:

res = [[1,2,3],[4,5,6],[7,8,9]]
res = res.map { |x| x[1..2] } 
# res == [[2, 3], [5, 6], [8, 9]]

Is there any function that works like that in JavaScript ?

Answer 1

You could check out Underscore.js Map helper function (there is also MapObject helper, similar to map, but works with objects): http://underscorejs.org/#map

_.map([1, 2, 3], function(num){ return num * 3; });
=> [3, 6, 9]
_.map({one: 1, two: 2, three: 3}, function(num, key){ return num * 3; });
=> [3, 6, 9]
_.map([[1, 2], [3, 4]], _.first);
=> [1, 3]

Failing that, you could try ES6 map object: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map

var kvArray = [["key1", "value1"], ["key2", "value2"]];

// Use the regular Map constructor to transform a 2D key-value Array into a map
var myMap = new Map(kvArray);

myMap.get("key1"); // returns "value1"

// Use the spread operator to transform a map into a 2D key-value Array.
alert(uneval([...myMap])); // Will show you exactly the same Array as kvArray

// Or use the spread operator on the keys or values iterator to get 
// an array of only the keys or values
alert(uneval([...myMap.keys()])); // Will show ["key1", "key2"]

If you decide on ES6, you will also need a transpiler such as Babel.

Hope that helps.

Answer 2

you can use https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map

For browsers that don't support the Array map method, here's an alternative implementation:

if (!Array.prototype.map) {
    Array.prototype.map = function(fun /*, thisp*/) {
        var len = this.length >>> 0;
        if (typeof fun != "function") {
            throw new TypeError();
        }

        var res = new Array(len);
        var thisp = arguments[1];
        for (var i = 0; i < len; i++) {
            if (i in this) {
                res[i] = fun.call(thisp, this[i], i, this);
            }
        }

        return res;
    };
}

or

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map#Polyfill