Avoid global variables, avoid new, avoid ==, avoid eval() Avoid Global Variables Minimize the use of global variables. This includes all data types, objects, and functions. Global variables and functions can be overwritten by other scripts. Use local variables instead, and learn how to use closures. Always Declare Local Variables All variables used in a function […]
Always use the same coding conventions for all your JavaScript projects. JavaScript Coding Conventions Coding conventions are style guidelines for programming. They typically cover: Naming and declaration rules for variables and functions. Rules for the use of white space, indentation, and comments. Programming practices and principles Coding conventions secure quality: Improves code readability Make code maintenance easier […]
“use strict”; Defines that JavaScript code should be executed in “strict mode”. The “use strict” Directive The “use strict” directive is new in JavaScript 1.8.5 (ECMAScript version 5). It is not a statement, but a literal expression, ignored by earlier versions of JavaScript. The purpose of “use strict” is to indicate that the code should be […]
Hoisting is JavaScript’s default behavior of moving declarations to the top. JavaScript Declarations are Hoisted In JavaScript, a variable can be declared after it has been used. In other words; a variable can be used before it has been declared. Example 1 gives the same result as Example 2: Example 1 x = 5; // Assign 5 to x […]
The break statement “jumps out” of a loop. The continue statement “jumps over” one iteration in the loop. The Break Statement You have already seen the break statement used in an earlier chapter of this tutorial. It was used to “jump out” of a switch() statement. The break statement can also be used to jump […]
Loops can execute a block of code as long as a specified condition is true. The While Loop The while loop loops through a block of code as long as a specified condition is true. Syntax while (condition) { code block to be executed } Example In the following example, the code in the […]
Conditional statements are used to perform different actions based on different conditions. Conditional Statements Very often when you write code, you want to perform different actions for different decisions. You can use conditional statements in your code to do this. In JavaScript we have the following conditional statements: Use if to specify a block of code to […]
A JavaScript Boolean represents one of two values: true or false. Boolean Values Very often, in programming, you will need a data type that can only have one of two values, like YES / NO ON / OFF TRUE / FALSE For this, JavaScript has a Boolean data type. It can only take the values true or false. The Boolean() Function You can […]
Math.random() Math.random() returns a random number between 0 (inclusive), and 1 (exclusive): Example Math.random(); // returns a random number Try it Yourself » Math.random() always returns a number lower than 1. JavaScript Random Integers Math.random() used with Math.floor() can be used to return random integers. Example Math.floor(Math.random() * 10); // returns a random integer from 0 to […]
The JavaScript Math object allows you to perform mathematical tasks on numbers. Example Math.PI; // returns 3.141592653589793 Try it Yourself » Math.round() Math.round(x) returns the value of x rounded to its nearest integer: Example Math.round(4.7); // returns 5 Math.round(4.4); // returns 4 Try it Yourself » Math.pow() Math.pow(x, y) returns the value of x to the power of […]
Set Date methods let you set date values (years, months, days, hours, minutes, seconds, milliseconds) for a Date Object. Set Date Methods Set Date methods are used for setting a part of a date: Method Description setDate() Set the day as a number (1-31) setFullYear() Set the year (optionally month and day) setHours() Set the […]
JavaScript Date Output By default, JavaScript will use the browser’s time zone and display a date as a full text string: Thu Jul 05 2018 12:12:01 GMT+0500 (Pakistan Standard Time) You will learn much more about how to display dates, later in this tutorial. Creating Date Objects Date objects are created with the new Date() constructor. There […]
The sort() method sorts an array alphabetically: Example var fruits = [“Banana”, “Orange”, “Apple”, “Mango”]; fruits.sort(); // Sorts the elements of fruits Try it Yourself » Reversing an Array The reverse() method reverses the elements in an array. You can use it to sort an array in descending order: Example var fruits = [“Banana”, “Orange”, “Apple”, “Mango”]; fruits.sort(); // First sort the elements of fruits fruits.reverse(); // Then reverse the […]
Converting Arrays to Strings The JavaScript method toString() converts an array to a string of (comma separated) array values. Example var fruits = [“Banana”, “Orange”, “Apple”, “Mango”]; document.getElementById(“demo”).innerHTML = fruits.toString(); Result Banana,Orange,Apple,Mango Try it Yourself » The join() method also joins all array elements into a string. It behaves just like toString(), but in addition you can specify the separator: Example var fruits = [“Banana”, “Orange”, “Apple”, “Mango”]; […]
JavaScript arrays are used to store multiple values in a single variable. Example var cars = [“Saab”, “Volvo”, “BMW”]; Try it Yourself » What is an Array? An array is a special variable, which can hold more than one value at a time. If you have a list of items (a list of car names, for example), storing […]
JavaScript has only one type of number. Numbers can be written with or without decimals. Example var x = 3.14; // A number with decimals var y = 3; // A number without decimals Try it yourself » Extra large or extra small numbers can be written with scientific (exponent) notation: Example var x = 123e5; // 12300000 var y = 123e-5; // 0.00123 JavaScript Numbers are […]
JavaScript strings are used for storing and manipulating text. JavaScript Strings A JavaScript string is zero or more characters written inside quotes. Example var answer = “It’s alright”; var answer = “He is called ‘Johnny’”; var answer = ‘He is called “Johnny”‘; Try it Yourself » String Length The length of a string is found in the built in property length: Example […]
HTML events are “things” that happen to HTML elements. When JavaScript is used in HTML pages, JavaScript can “react” on these events. HTML Events An HTML event can be something the browser does, or something a user does. Here are some examples of HTML events: An HTML web page has finished loading An HTML input field was changed An […]
Scope determines the accessibility (visibility) of variables. JavaScript Function Scope In JavaScript there are two types of scope: Local scope Global scope JavaScript has function scope: Each function creates a new scope. Scope determines the accessibility (visibility) of these variables. Variables defined inside a function are not accessible (visible) from outside the function. Local JavaScript […]
JavaScript Data Types JavaScript variables can hold many data types: numbers, strings, objects and more: var length = 16; // Number var lastName = “Johnson”; // String var x = {firstName:”John”, lastName:”Doe”}; // Object The Concept of Data Types In programming, data types is an important concept. To be able to operate on variables, it is important to know something about the type. Without […]
