Javascript callback function get parent variable value

Question

function foo(callback){
    var a = 1;
    
    return callback();
}

foo(function(){ 
    if ( a == 1 ) { alert(a); }
});

I try to make a callback can access parent var, but I get undefine

anyone know how to achieve this

Answer 1

Make a an argument and pass it to the callback:

function foo(callback){
    var a = 1;
    
    return callback(a);
}

foo(function(a){ 
    if ( a == 1 ) { alert(a); }
});

Answer 2

Try sending variable "a" in callback function as parameter.

 function foo(callback){ var a = 1; return callback(a); } foo(function(a){ if ( a == 1 ) { alert(a); } });