javascript - forEach on a 'new Array' isn't doing what I expect -

i'm learning how use js higher-order functions (map, foreach, reduce, etc), , have stumbled confusion. i'm trying write simple 'range' function, can't seem populate output array. goal:

range(1, 4) // [1, 2, 3, 4] 

i'm getting this:

[undefined × 4] 

here code:

 function range(num1, num2) {       var rangearr = new array((num2 + 1) - num1);       return rangearr.map(function(e, i, arr) {return arr[i] = num1 + i});     } 

what missing here? far can tell problem appears have way i'm utilizing 'new array', beyond i'm lost.

oh, , here's part confuses me. works fine:

function bleck() {     var blah = [1, 2, 3, 4];     var x = 'wtf';     return blah.map(function(e, i, arr) {return arr[i] = x}) }  ["wtf", "wtf", "wtf", "wtf"] 

thanks!!

the foreach method iterates on the indices of array. interestingly enough, when create new array via new array(n), contains no indices @ all. instead, sets .length property.

> var = new array(3); > console.info(a) [] > console.info([undefined, undefined, undefined]) [undefined, undefined, undefined] 

mdn describes foreach, , states:

foreach executes provided callback once each element of array assigned value. not invoked indexes have been deleted or elided.

here's neat technique array empty, existing, indices.

var = array.apply(null, array(3)); 

this works because .apply "expands" elided elements proper arguments, , results ends being array(undefined, undefined, undefined).