Question

In a Javascript program I have an object with the following two (simplified) functions:

this.do_A = function() {
    var nothing_changed = false;
    while (!nothing_changed) {
        nothing_changed = true;
        for (var column=0; column<this.columns; column++) {
            for (var row=0; row<this.rows; row++) {
                nothing_changed = nothing_changed && this.do_B(row, column);
            }
        }
    } 
}

this.do_B = function(row, column) {
    nothing_changed = true;
    if (this[row][column] == null) {
        nothing_changed = false;
    }
    return nothing_changed;
} 

When running this code something very strange happens when do_B returns false, and hence nothing_changed becomes false – when reaching again the

for (var row=0; row<this.rows; row++)

line, the row variable becomes immediately this.rows and hence the inner loop terminates. Moreover, it happens in the subsequent runs of the outer loops – row is initialized to be 0, then becomes this.rows immediately and the inner loop ends again.

I have no reason what can cause this. I have tried simplifying the functions as much as possible and it keeps happening.

Answer 1

for (var row=0; row<this.rows; row++)
{
  nothing_changed = nothing_changed && this.do_B(row, column);
}  

When this.do_B(row, column) returns false, nothing_changed will be false
, and when it loops again and reaches nothing_changed = nothing_changed && this.do_B(row, column), because nothing_changed is false, the second expression this.do_B(row, column) will not be evaluated, so nothing_changed will always be false until row reaches this.rows.