JavaScript Note Two

2015-06-15 215 words 2 minutes

Contents

Anything that produces a value is an expression in JavaScript
The function Number converts a value to a number.
The isNaN function is a standard JavaScript function that returns true only if the argument it is given is NaN.

Variables declared outside of any function are called global, because they are visible throughout the program.
Functions can be created inside other functions, producing several degrees of locality.
In JavaScript, functions are the only things that create a new scope.
The next version of JavaScript will introduce a let keyword, which works like var but creates a variable that is local to the enclosing block, not the enclosing function.
Function declarations are not part of the regular top-to-bottom flow of control. They are conceptually moved to the top of their scope and can be used by all the code in that scope.
JavaScript is extremely broad-minded about the number of arguments you pass to a function. If you pass too many, the extra ones are ignored. If you pass too few, the missing parameters simply get assigned the value undefined.

Being able to reference a specific instance of local variables in an enclosing function—is called closure.
A function that “closes over” some local variables is called a closure.