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In this article I will explain importance of var in Javascript Step 1: Create an aspx page with a button control. Button will invoke fnCall javascript
<asp:Button ID="btnTest" Text="Test Javascript" OnClientClick="return fnCall();" runat="server" />
Step 2: Add below javascript on the same page < script language="javascript" type="text/javascript">
function fnCall() {
for (x = 0; x < 10; x++) {
fnCall1();
alert(x);
}
return false;
} function fnCall1() {
for (x = 0; x < 10; x++) {
//your code
}
} </ script>
Step 3: Now run the page and click on Button, you will notice that alert is coming only once with value 10 insted of 10 alerts with 1 to 10.
Actually this behavious is quite obvious because x is global. If the variable doesn’t have var, javascript treats it as a global variable. Since the x doesn’t have var, javascript treats it as a global variable. When fnCall1 is called, loop increments the value of x to 10 making fnCall to run only once.
To resolve the issue, declare x with var
<script language="javascript" type="text/javascript">
function fnCall() {
for (var x = 0; x < 10; x++) {
fnCall1();
alert(x);
}
return false;
}function fnCall1() {
for (x = 0; x < 10; x++) {
//your code
}
} </ script>
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