How to use loop for on javascript and use var in loop for?

Question

How to use loop for on javascript and use var in loop for ?

When click button. It's will be auto fill value to input type text with loop for

But not work , How can i do that ?

http://jsfiddle.net/fNPvf/16471/

function change(){ 
 var price_start = document.getElementById('price_start').value;
 for (i = 1; i <= 14; i++) { 
 constance_val = i*2;
 price_month_+i+ = price_start*constance_val;
 document.getElementById('price_month_'+i+).value = price_month_+i+; 
 }
}

• h2ooooooo: possible duplicate of Use dynamic variable names in JavaScript (or you know.. use an array or a regular variable? Look in your console and you'll realize that you can't name a variable price_month_+i+)
• Luke: also, your i is currently an implied global
• Arun P Johny: jsfiddle.net/arunpjohny/wzd51poL/1

Answer 1

You can't use i+ as a variable as it gets parsed as addition and will cause syntax errors. And you don't even need that part. You did it correctly for constance_val, but there's no need to keep values for price_month_+i because you only need them inside each loop iteration.

Here is a fixed working example, slightly optimized:

function change(){ 
 var price_start = document.getElementById('price_start').value;
 for (var i = 1; i <= 14; i++) { 
 document.getElementById('price_month_'+i).value = price_start * i * 2;
 }
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="submit" id="byBtn" value="Change" onclick="change()"/>
 
<input type="text" id="price_start" value="5">
<br>
<br>
<input type="text" id="price_month_1">
<br>
<br>
<input type="text" id="price_month_2">
<br>
<br>
<input type="text" id="price_month_3">
<br>
<br>
<input type="text" id="price_month_4">
<br>
<br>
<input type="text" id="price_month_5">
<br>
<br>
<input type="text" id="price_month_6">

Answer 2

you had syntactic errors in your code ... and you should declare all variables as var

function change(){ 
 var price_start = document.getElementById('price_start').value;
 for (var i = 1; i <= 14; i++) { 
 var constance_val = i*2;
 var price_month = price_start*constance_val;
 document.getElementById('price_month_'+i).value = price_month; 
 }
}

btw. since your button does not submit anything you should probably use <input type="button"> (or <button type="button">) instead of <input type="submit">