javascript is there a way to increment a for loop with a variable

Question

I have a function -- let's call it test(arg1,arg2), called from program1, which does a number of things and is working correctly. Within test there is a loop:

for(j=1;j<=top;j++) {
   stuff happens based on j 
}

I would like to call test(arg1,arg2) from a different program, say program2. Everything about test is the same for these two programs except the for loop. For program2 I need that loop to be

for(j=2;j<=top;j+=2) {
   stuff happens based on j 
}

Otherwise everything else is exactly the same.

The second argument, arg2 tells us whether the script was called from program1 or program2. But I can't figure out how to write a variable "for" statement. I tried an if statement based on arg2

var jstart = 1 or 2 
var jincr = '++' or '+=2'

and then wrote the loop as

for(j=jstart;j<=top;j jincr) {

This did not work, although it is an approach that works in other languages.

Can someone suggest I way I can do this without writing an entirely separate script for the two cases?

Couldn't you just put if(jStart == 1) { j++; } else { j += 2; }? Evaling code just to accomplish something like this is extremely hacky, even if other languages allow it (JS allows it too). — Carcigenicate
– Carcigenicate, Commented May 27, 2018 at 0:34

Deblaton Jean-Philippe · Accepted Answer · 2018-05-27 00:34:35Z

3

As simple as that

jstart = 1 // or 2
jincr = 1 // or 2;
for(j=jstart;j<=top;j += jincr) {

answered May 27, 2018 at 0:34

Deblaton Jean-Philippe

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1 Comment

Betty Mock Over a year ago

This is very nice.

Damon · Accepted Answer · 2018-05-27 00:59:58Z

1

The most reusable way would be to put your loop in a function that accepts increment as an argument:

function doStuff (inc) {
  for(var j = inc; j <= top; j += inc) {
    // stuff happens based on j 
  }
}

// Program 1
doStuff(1)

// Program 2
doStuff(2)

answered May 27, 2018 at 0:59

Damon

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1 Comment

Betty Mock Over a year ago

For my situation it is the easiest, although the answer below is very helpful also.

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