javascript-cheat-sheet.md

JavaScript: Overview

Asynchronous JavaScript

Asynchronous means once a request is made, it doesn't wait for the response in order to move to the next step. Instead, it keeps running all tasks at once. Asynchronous JavaScript is often used with AJAX calls. See also Synchronous JavaScript.

JavaScript is typically synchronous, where it performs one task at a time, finishes that task before moving on to the next task.

##Closures Closures are functions that refer to variables that are used locally, but defined in an enclosing scope. These functions remember the environment they were created in.

Looping

Loops are a way to do something repeatedly. JavaScript has several different methods of achieving this.

for statement

A for statement is usually used when you need to increment a value within an expression.

for (var i = 0; i > 10; i++) {
  console.log(i);
}

do...while statement

A do...while statement repeats until a specific condition evaluates to false.

var i = 10;
do {
  i++;
  console.log(i);
} while (i < 40);

while statement

A while statement executes as long as a specified condition evaluates to true.

var i = 2;
while (i < 5) {
  i++;
  console.log(i);
}

break statement

The break statement is used to terminate a loop.

for (var i = 0; i < a.length; i++) {
  if (a[i] == 5) {
    break;
  }
}

Promises

A promise is the result of an asynchronous operation. It is a placeholder for the successful result value or reason for failure will occur.

##Scope Scope relates to the variables you have access to within your code. There are two different types of scope that are possible:

• Local Scope: variables that are only accessible within a specific function

• Global Scope: variables that can be accessed anywhere within your code

Synchronous JavaScript

Synchronous JavaScript is when the code performs one task at a time. Once it has finished one task, it moves on to the next one. See also Asynchronous JavaScript.