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Asked: 2026-05-11T09:41:17+00:00

Consider the following piece of code. <html> <body> <script> var x = 5; //globally

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Consider the following piece of code. 

<html> <body> <script>   var x = 5; //globally declared function showX()  {        alert('x='+x); //trying to display global value        var x=10; //trying to create and initialize a local x } </script> <input type = 'button' value='Show X' onclick='showX()'>  </body> </html>

The alert statement shows ‘x=undefined’. And doesn’t print the global value of x as expected. An equivalent java code would display 5! So, is it a bug? If not then how does one explain that behavior?

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  1. The ECMAScript Specification says in section 12.2:

    If the variable statement occurs inside a FunctionDeclaration, the variables are defined with function-local scope in that function, as described in s10.1.3. Otherwise, they are defined with global scope (that is, they are created as members of the global object, as described in 10.1.3) using property attributes { DontDelete}. Variables are created when the execution scope is entered. A Block does not define a new execution scope. Only Program and FunctionDeclaration produce a new scope. Variables are initialised to undefined when created. A variable with an Initialiser is assigned the value of its AssignmentExpression when the VariableStatement is executed, not when the variable is created.

    So it’s not a bug – the local variable is created when the function is entered.

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