js recursive function changing variables unexpectedly

Question

Here is a function I wrote in Javascript to illustrate the problem I'm having.

function test(x,depth){
    for (n=0;n<x;n++){
        console.log(x.toString()+" "+depth.toString()+" "+n.toString())
        test(x-1,depth+1)
        console.log(x.toString()+" "+depth.toString()+" "+n.toString())
    }
}


test(4,0)

here is my console output:

why is the variable n effected by calling test(x-1,depth+1)? n is not passed as a parameter.

Thanks

T.J. Crowder · Accepted Answer · 2017-11-27 16:47:53Z

3

n is global, created via The Horror of Implicit Globals* the first time you assign a value to it (n=0), and so that one global variable is used by all calls to test. You need to declare it within test for it to be local (and thus for each call to have its own copy). (E.g., add var or, in ES2015+, let.)

* (That's a post on my anemic little blog.)

answered Nov 27, 2017 at 16:47

T.J. Crowder

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Comments

Suren Srapyan · Accepted Answer · 2017-11-27 16:51:17Z

1

Your n is a global variable because it is declared without let, var or const. It is actually window.n. Means that each recursive called function uses the single property. Declare it via let or var to make each function has its own n variable.

function test(x,depth){
    for (let n = 0; n < x; n++){
        console.log(x.toString()+" "+depth.toString()+" "+n.toString())
        test(x-1,depth+1)
        console.log(x.toString()+" "+depth.toString()+" "+n.toString())
    }
}


test(4,0)

edited Nov 27, 2017 at 16:51

answered Nov 27, 2017 at 16:48

Suren Srapyan

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