javascript - Create Simple Dynamic Array

Question

What\'s the most efficient way to create this simple array dynamically.

var arr = [ \"1\", \"2\", \"3\", \"4\", \"5\", \"6\", \"7\", \"8\", \"9\", \"10\"];
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Answer 1

misread the question, corrected. Try:

var myNumber = 100,
    myarr = (function arr(i){return i ? arr(i-1).concat(i) : [i]}(myNumber));

Just for fun, if you extend Array like this:

Array.prototype.mapx = function(callback){
  return String(this).split(',').map(callback);
}

You could use:

var myNum = 100, 
    myarr = new Array(myNum).mapx(function(el,i){return i+1;});

Answer 2

With ES2015, this can be achieved concisely in a single expression using the Array.from method like so:

Array.from({ length: 10 }, (_, idx) => `${++idx}`)

The first argument to from is an array like object that provides a length property. The second argument is a map function that allows us to replace the default undefined values with their adjusted index values as you requested. Checkout the specification here

Answer 3

var arr = [];
for(var i=1; i<=mynumber; i++) {
   arr.push("" + i);
}

This seems to be faster in Chrome, according to JSPerf, but please note that it is all very browser dependant.

There's 4 things you can change about this snippet:

1. Use for or while.
2. Use forward or backward loop (with backward creating sparse array at beginning)
3. Use push or direct access by index.
4. Use implicit stringification or explicitly call toString.

In each and every browser total speed would be combination of how much better each option for each item in this list performs in that particular browser.

TL;DR: it is probably not good idea to try to micro-optimize this particular piece.

Answer 4

updated = > june 2020

if are you using node js you can create or append a string value with " ," operator then inside the loop you can

for (var j = 0; j <= data.legth -1; j++) {
                    lang += data.lang  +", " ;

                }

 var langs = lang.split(',')
 console.log("Languages =>",  lang, typeof(lang), typeof(langs), langs) 
 console.log(lang[0]) // here access arrary by index value
            

you can see the type of string and object

Answer 5

I hope you have to get last element from array variable so my solution

var arr = [ "1", "2", "3", "4", "5", "6", "7", "8", "9", "10"];
var mynumber = arr [arr .length - 1];
//var mynumber = 10;

Answer 6

Update: micro-optimizations like this one are just not worth it, engines are so smart these days that I would advice in the 2020 to simply just go with var arr = [];.

Here is how I would do it:

var mynumber = 10;
var arr = new Array(mynumber);

for (var i = 0; i < mynumber; i++) {
    arr[i] = (i + 1).toString();
}

My answer is pretty much the same of everyone, but note that I did something different:

• It is better if you specify the array length and don't force it to expand every time

So I created the array with new Array(mynumber);