Implied Globals: Any variable you don't declare becomes a property of the global object in JavaScript.
Two examples for demonstration:
1)
function sum(x, y) { result = x + y; // implied global return result; } sum(1,2); // 3 console.log(this.result); // 3 console.log(typeof result); // "number" delete result; // true console.log(typeof result); // "undefined"
2)
function foo() { // a is local but b is implied global. // It's because of the right-to-left evaluation. var a = b = 0; } foo(); console.log(this.b); // 0 console.log(this.a); // "undefined" console.log(typeof b); // "number" delete b; // true console.log(typeof b); // "undefined"