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Feb 11, 2013 · @Amberlamps your .reduce example is OK, but IMHO it still falls a long way short of the convenience of a .map for Objects, since your .reduce callback not only has to match the way that .reduce works, but also requires that myObject be available in the lexical scope.
Mar 28, 2019 · Array.prototype.map() is a function that transforms Arrays. It maps one Array to another Array. The most important part of its function signature is the callback. The callback is called on each item in the Array and what that callback returns is what is put into the new Array returned by map. It does not do anything special with what gets returned.
The third argument of the callback function exposes the array on which map was called upon The second argument of Array.map() is a object which will be the this value for the callback function. Keep in mind that you have to use the regular function keyword in order to declare the callback since an arrow function doesn't have its own binding to the this keyword.
The map's inner mapping function can just return() (ie. no return val) rather than the invalid continue() , which will insert an undefined value as that element. That's consistent with the map() function's design: map the processed array to a returned array 1:1 by values. Otherwise use flatMap() as described in an answer below. –
Oct 27, 2023 · Maps provide three ways to get iterators for their contents: keys - Iterates the keys in the map; values - Iterates the values; entries - Iterates the key and values, giving you [key, value] arrays (this is the default) As Nina notes, Maps also provide forEach, which loops through their contents giving the callback the value, key, and map as ...
If you'd like to map over all elements concurrently: function asyncMap(arr, fn) { return Promise.all(arr.map(fn)); } If you'd like to map over all elements non-concurrently (e.g. when your mapping function has side effects or running mapper over all array elements at once would be too resource costly): Option A: Promises
You can easily pass a second parameter to the map function. The following method is widely used to pass this parameter which generally gets hidden during the call: values.map(function(x , this) { return x*x + this.adjustment; }); var adjustment = 1; var values = [1,2,3,4] values.map(function(x , adjustment) { return x*x + adjustment; }); OR
Aug 28, 2019 · You cannot conditionally map with the .map() function alone, however you can use .filter() to achieve what you require. Calling filter will return a new array where each item in the new array satisfies your filtering criteria (ie people.available === true ).
@user3201696 it would pretty much look like .filter(function(obj) { return obj.selected; }).map(function(obj) { return obj.id1 }); That would create a new array which only contains the values of the id1 properties. –
Sep 4, 2012 · @Vadorequest I did post the question when I was js newbie, Array.prototype.map was not supposed to be used that way at all, it is a helper method for a whole different usecase where you want to transform every element of a given array into a different variant. So, when it's going to be about "every element", you would never need a "break" statement, if you need a break statement it means maybe you don't need a map.
