The difference between adding var and not adding var when javascript defines a variable

1. The external is the global, and the internal is the local variable.

2. Add var as a local variable (within the method), and leave var as a global variable (after the method has been used once)

<script type="text/javascript"> 

var golbe="global"; 

test(); 

function test(){ 

     var local="local"; 

    document.write(golbe); 

    document.write(local); 

}

document.write(golbe); 

document.write(local);

</script>

In the test method above, when var of local is removed, local becomes a global variable, but if local is not used locally, local is not valid as a global variable.

To verify this, I comment out the code inside the test method where only 1 USES the local variable.

Conclusion: global variables can not declare var function variables must declare var, the definition of global variables without or without the var keyword does not matter; But if you define a local variable without the var keyword, the javascript interpreter will interpret it as a global variable.