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JavaScript Operators
JavaScript OperatorsExampleAssign values to variables and add them together:var x = 5; // assign the value 5 to xvar y = 2; // assign the value 2 to yvar z = x + y; // assign the value 7 to z (x + y)The assignment operator (=) assigns a value to a variable.Assignmentvar x = 10;The addition operator (+) adds numbers:Addingvar x = 5;var y = 2;var z = x + y;The multiplication operator (*) multiplies numbers.Multiplyingvar x = 5;var y = 2;var z = x * y;
Jay Kakadiya
JavaScript String Operators
JavaScript String OperatorsThe + operator can also be used to add (concatenate) strings.Examplevar txt1 = "John";var txt2 = "Doe";var txt3 = txt1 + " " + txt2;The result of txt3 will be:John DoeThe += assignment operator can also be used to add (concatenate) strings:Examplevar txt1 = "What a very ";txt1 += "nice day";The result of txt1 will be:What a very nice dayWhen used on strings, the + operator is called the concatenation operator.Adding Strings and NumbersAdding two numbers, will return the sum, but adding a number and a string will return a string:Examplevar x = 5 + 5;var y = "5" + 5;var z = "Hello" + 5;The result of x, y, and z will be:1055Hello5If you add a number and a string, the result will be a string!
Arithmetic Operations
Arithmetic OperationsA typical arithmetic operation operates on two numbers.The two numbers can be literals:Examplevar x = 100 + 50;or variables:Examplevar x = a + b;or expressions:Examplevar x = (100 + 50) * a;
JavaScript Assignment
JavaScript AssignmentThe = assignment operator assigns a value to a variable.Assignmentvar x = 10;The += assignment operator adds a value to a variable.Assignmentvar x = 10;x += 5;The -= assignment operator subtracts a value from a variable.Assignmentvar x = 10;x -= 5;The *= assignment operator multiplies a variable.Assignmentvar x = 10;x *= 5;The /= assignment divides a variable.Assignmentvar x = 10;x /= 5;The %= assignment operator assigns a remainder to a variable.Assignmentvar x = 10;x %= 5;
JavaScript Data Types
JavaScript Data TypesJavaScript variables can hold many data types: numbers, strings, objects and more:var length = 16; // Numbervar lastName = "Johnson"; // Stringvar x = {firstName:"John", lastName:"Doe"}; // ObjectThe Concept of Data TypesIn programming, data types is an important concept.To be able to operate on variables, it is important to know something about the type.Without data types, a computer cannot safely solve this:var x = 16 + "Volvo";Does it make any sense to add "Volvo" to sixteen? Will it produce an error or will it produce a result?JavaScript will treat the example above as:var x = "16" + "Volvo";When adding a number and a string, JavaScript will treat the number as a string.Examplevar x = 16 + "Volvo";Examplevar x = "Volvo" + 16;JavaScript evaluates expressions from left to right. Different sequences can produce different results:JavaScript:var x = 16 + 4 + "Volvo";Result:20VolvoJavaScript:var x = "Volvo" + 16 + 4;Result:Volvo164
JavaScript Types are Dynamic
JavaScript Types are DynamicJavaScript has dynamic types. This means that the same variable can be used to hold different data types:Examplevar x; // Now x is undefinedx = 5; // Now x is a Numberx = "John"; // Now x is a StringJavaScript StringsA string (or a text string) is a series of characters like "John Doe".Strings are written with quotes. You can use single or double quotes:Examplevar carName1 = "Volvo XC60"; // Using double quotesvar carName2 = 'Volvo XC60'; // Using single quotesYou can use quotes inside a string, as long as they don't match the quotes surrounding the string:Examplevar answer1 = "It's alright"; // Single quote inside double quotesvar answer2 = "He is called 'Johnny'"; // Single quotes inside double quotesvar answer3 = 'He is called "Johnny"'; // Double quotes inside single quotesYou will learn more about strings later in this tutorial.JavaScript NumbersJavaScript has only one type of numbers.Numbers can be written with, or without decimals:Examplevar x1 = 34.00; // Written with decimalsvar x2 = 34; // Written without decimalsExtra large or extra small numbers can be written with scientific (exponential) notation:Examplevar y = 123e5; // 12300000var z = 123e-5; // 0.00123Try it yourself »You will learn more about numbers later in this tutorial.JavaScript BooleansBooleans can only have two values: true or false.Examplevar x = 5;var y = 5;var z = 6;(x == y) // Returns true(x == z) // Returns falseBooleans are often used in conditional testing.You will learn more about conditional testing later in this tutorial.JavaScript ArraysJavaScript arrays are written with square brackets.Array items are separated by commas.The following code declares (creates) an array called cars, containing three items (car names):Examplevar cars = ["Saab", "Volvo", "BMW"];
JavaScript Objects
JavaScript ObjectsJavaScript objects are written with curly braces {}.Object properties are written as name:value pairs, separated by commas.Examplevar person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};The object (person) in the example above has 4 properties: firstName, lastName, age, and eyeColor.You will learn more about objects later in this tutorial.The typeof OperatorYou can use the JavaScript typeof operator to find the type of a JavaScript variable.The typeof operator returns the type of a variable or an expression:Exampletypeof "" // Returns "string"typeof "John" // Returns "string"typeof "John Doe" // Returns "string"Exampletypeof 0 // Returns "number"typeof 314 // Returns "number"typeof 3.14 // Returns "number"typeof (3) // Returns "number"typeof (3 + 4) // Returns "number"
Undefined
UndefinedIn JavaScript, a variable without a value, has the value undefined. The type is also undefined.Examplevar car; // Value is undefined, type is undefinedAny variable can be emptied, by setting the value to undefined. The type will also be undefined.Examplecar = undefined; // Value is undefined, type is undefinedEmpty ValuesAn empty value has nothing to do with undefined.An empty string has both a legal value and a type.Examplevar car = ""; // The value is "", the typeof is "string"
Difference Between Undefined and Null
Difference Between Undefined and Nullundefined and null are equal in value but different in type:typeof undefined // undefinedtypeof null // objectnull === undefined // falsenull == undefined // true
Primitive Data
Primitive DataA primitive data value is a single simple data value with no additional properties and methods.The typeof operator can return one of these primitive types:stringnumberbooleanundefinedExampletypeof "John" // Returns "string"typeof 3.14 // Returns "number"typeof true // Returns "boolean"typeof false // Returns "boolean"typeof x // Returns "undefined" (if x has no value)Complex DataThe typeof operator can return one of two complex types:functionobjectThe typeof operator returns "object" for objects, arrays, and null.The typeof operator does not return "object" for functions.Exampletypeof {name:'John', age:34} // Returns "object"typeof [1,2,3,4] // Returns "object" (not "array", see note below)typeof null // Returns "object"typeof function myFunc(){} // Returns "function"
JavaScript Functions
JavaScript FunctionsA JavaScript function is a block of code designed to perform a particular task.A JavaScript function is executed when "something" invokes it (calls it).Examplefunction myFunction(p1, p2) { return p1 * p2; // The function returns the product of p1 and p2}JavaScript Function SyntaxA JavaScript function is defined with the function keyword, followed by a name, followed by parentheses ().Function names can contain letters, digits, underscores, and dollar signs (same rules as variables).The parentheses may include parameter names separated by commas:(parameter1, parameter2, ...)The code to be executed, by the function, is placed inside curly brackets: {}function name(parameter1, parameter2, parameter3) { // code to be executed}Function parameters are listed inside the parentheses () in the function definition.Function arguments are the values received by the function when it is invoked.Inside the function, the arguments (the parameters) behave as local variables.A Function is much the same as a Procedure or a Subroutine, in other programming languages.
JavaScript Objects
JavaScript ObjectsReal Life Objects, Properties, and MethodsIn real life, a car is an object.A car has properties like weight and color, and methods like start and stop:JavaScript ObjectsYou have already learned that JavaScript variables are containers for data values.This code assigns a simple value (Fiat) to a variable named car:var car = "Fiat";Objects are variables too. But objects can contain many values.This code assigns many values (Fiat, 500, white) to a variable named car:var car = {type:"Fiat", model:"500", color:"white"};