JavaScript：For-Loop无法运行？

Question

Why the for loop does not run?

• The Error-Console is empty
• The function countfiles return a whole number
• parseInt(countfiles()) also not work too

Here my Code:

function set_default_value() {
    var element = document.getElementsByName('fields');
    for (var i = countfields(); i < element.length; ++i) {
        element[i].value = "default";
    }
}

Why does not run?

EDIT:

• Countfields is lower than element.length
• The function is running
• Countfield return a number like 0, 1, 2, 3, ...

Here's the function countfields

function countfields() {
    var field_counter = 0;
    for (var i = 0; i < 50; i++) {
        if (typeof document.getElementsByName('other_fields')[i] != "undefined") {
        var field_counter = field_counter + 1; 
        }
    }
    return field_counter; 
}

Answer 1

@varunachar touched on the issue in one of his comments:

The number returned by countfields could be greater than element.length

In this line:

for (var i = countfields(); i < element.length; ++i)

Read this i < element.length as "as long as i is less than element.length , do stuff" . Or, if countfields() is equal or greater, nothing happens.

1 other_fields : http://jsfiddle.net/D5ZHV/ works
6 other_fields : http://jsfiddle.net/Ay6BN/ does not work

Answer 2

Change

        var field_counter = field_counter + 1; 

To

        field_counter = field_counter + 1; 

In countfields() function. You are declaring field_counter inside the for loop which is wrong

Answer 3

function countfields() {
    var field_counter = 0;
    for(var i = 0; i < 50; i++) {
        if(typeof document.getElementsByName('other_fields')[i] != "undefined") {
        var field_counter = field_counter + 1; } }
    return field_counter; }

var always define the scope of the variable. Inside the if doing var field_counter will create a variable with scope inside the if-statement.

you should write as

field_counter = field_counter + 1; 

If you test your countfields() it should always return 0;

Also try doing console.log(elements)