var x = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
         11, 12, 13, 14, 15, 16, 17, 18, 19, 20];

var x = [];
for (var i=1;i<=20;i++) {
  x.push(i);
}

var x = [], i = 1, endInt = 20;
while (i <= endInt) {
  x.push(i);
  i++;
}

function range1(i){return i?range1(i-1).concat(i):[]}

function range1(i){var x=[];var i=1;while(x.push(i++)<i){};return x}

> range1(5)
[1, 2, 3, 4, 5]

> Array(5).fill().map((x,i)=>i)
[0, 1, 2, 3, 4]

> Array.from(Array(5),(x,i)=>i)
[0, 1, 2, 3, 4]

x = []; //normally would use var here
i = 1;  //normally would use var here
while(x.push(i++)<20){}

//at this point, x = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

x=[];i=1;while(x.push(i++)<20);

Array.from(new Array(20), (x,i) => i+1)

Array.from(new Array(5), (x,i) => i+5)

var a=[],b=10;while(b--)a[b]=b+1

var array=[],length=20,start=5;while(length--)array[length]=length+start

var array=[],end=30,start=25,a=end-start+1;while(a--)array[a]=end--

for(var a=[],b=20;b>0;b--,a[b]=b+1)

for(var a=[],b=0;b<20;b++,a[b]=b+1)

function range(a,b,c,d){d=[];c=b-a+1;while(c--)d[c]=b--;return d}

var range = function (start, end) {
    var arr = [];

    while (start <= end) {
        arr.push(start++)
    }

    return arr;
};

var i=0, arr = [];
while (i++<20){
  arr.push(i);
}

var i,arr; while (i=i||1, (arr=arr||[]).push(i++)<20){}

function createNumArray(a, b) {
   var arr = [],
       i = a;

    while((arr[arr.length] = i) < b) {i++}
    return arr;
}

var arr = createNumArray(1, 20);

var x=[],i=0
while(i<20)
  x[i]=i+++1

var x=[],i=0
while(i<20)
  x[i]=++i

function range(s,e){var x=[];while(s<e+1)x.push(s++);return x}

var x = [];
for (var i=1;i<=20;i++) {
  x.push(i);
}

var i = 0;
var x = [];
while (i++ < 20) x.push(i);

Array.prototype.range = function(start, end) {
    if (!this.length) {
        while (end >= start) {
            this.push(start++);
        }
    } else {
        throw "You can only call 'range' on an empty array";
    }
    return this;
};

var array = [].range(1, 20);

test = [1..20]

alert test

var test;
test = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20];
alert(test);