Member Avatar for nouth

my previous question about this dealt with global vars
but unfortunatley the window of opportunitys doesn't work with this next example because it alerts 4 times instead of only 1

test("a","b","c");
function test(var0,var1,var2,var3) {
    for(var i=0; i<4; i++) {
        if(window["var"+i]===undefined) {alert("test");}
    }
}

this may not be very clear so I will try again
this time I want it to alert all three vars

test("a","b","c");
function test(var0,var1,var2) {
    for(var i=0; i<3; i++) {
        alert(window["var"+i]);
    }
}

how can I achieve the identical results as with the window["str"+var] from within a function?

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  • Latest Post Latest Post by felgall

Dani AI

Generated

Short answer: you can't turn a string into the name of a local variable the way you can with globals (window["..."]). Local parameter names are lexical identifiers, not properties on the global object. As hinted, treat the incoming values as a collection rather than trying to reconstruct local names.

A clean modern approach is to use rest parameters and work with an array of values:

function test(...values) {
  for (let i = 0; i < values.length; i++) {
    alert(values[i]);
  }
}

If you specifically need string-keyed lookup (e.g. you want to query "var0", "var1" by name), build or receive an object that maps those names to values:

function test(a, b, c) {
  const byName = { var0: a, var1: b, var2: c };
  alert(byName['var1']); // dynamic lookup works on the object
}

Or simply pass an array or object in the first place:

test(['a','b','c']);          // treat as ordered list
test({var0:'a',var1:'b'});    // treat as named map

Notes and cautions:

  • window["var"+i] only finds globals; local params won't be there.
  • You can convert the old-style arguments to a real array with Array.from(arguments) or the spread operator, but prefer rest parameters in new code.
  • Avoid using eval to resolve local names dynamically — it's slow and unsafe.
  • Make loops use the actual length (values.length or Object.keys(map).length) to avoid off‑by‑one alerts like the four-alert symptom you saw.

These patterns keep code clear, safe, and easy to maintain compared with trying to construct local variable names at runtime.

Member Avatar for felgall

All of the values passed to a function are stored in "arguments".

test("a","b","c");
function test(var0,var1,var2) {
    for(var i=0; i<3; i++) {
        alert(arguments[i]);
    }
}
Edited by felgall
commented: thanks :) +1
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