In this tutorial, let us discuss how to validate a given number in JavaScript. Users can follow the syntax below each method to use it. Using regular expression The method tests or matches the regular expression with the input. Syntax /\D/.test(input); input.match(/^[0-9]*$/); If the input is a number, the test returns true. Example The program succeeds in all cases except for "30", [], and "". Number validation using regular expression Validate ... Read More

To add a number of months to a date, first get the month using getMonth() method and add a number of months.ExampleYou can try to run the following code to add a number of monthsLive Demo                    var d, e;          d = new Date();          document.write(d);          e = d.getMonth()+1;          document.write("Incremented month = "+e);          

Function DeclarationThe “function” keyword declares a function in JavaScript. To define a function in JavaScript use the “function” keyword, followed by a unique function name, a list of parameters (that might be empty), and a statement block surrounded by curly braces.Here’s an example −function sayHello(name, age) {    document.write (name + " is " + age + " years old."); }Function ExpressionFunction Expression should not start with the keyword “function”. Functions defined can be named or anonymous.Here are the examples −//anonymous function expression var a = function() {    return 5; }Or//named function expression var a = function bar() {    return 5; }

Double equals (==) is abstract equality comparison operator, which transforms the operands to the same type before making the comparison. For example,5 ==  5       //true '5' == 5      //true 5 == '5'      //true 0 == false    //trueTriple equals (===) are strict equality comparison operator, which returns false for different types and different content.For example,5 === 5  // true 5 === '5' // false var v1 = {'value':'key'}; var v2 = {'value': 'key'}; v1 === v2 //false

ExampleTo parse JSON object in JavaScript, implement the following code −                    myData = JSON.parse('{"event1":{"title":"Employment period","start":"12\/29\/2011 10:20 ","end":"12\/15\/2013 00:00 "},"event2":{"title":"Employment period","start":"12\/14\/2011 10:20 ","end":"12\/18\/2013 00:00 "}}')          myArray = []          for(var e in myData){             var dataCopy = myData[e]             for(key in dataCopy){                if(key == "start" || key == "end"){                   dataCopy[key] = new Date(dataCopy[key])                }             }             myArray.push(dataCopy)          }          document.write(JSON.stringify(myArray));          

The conditional operator or ternary operator first evaluates an expression for a true or false value and then executes one of the two given statements depending upon the result of the evaluation.S.NoOperator & Description1? : (Conditional )If Condition is true? Then value X: Otherwise value YExampleYou can try to run the following code to understand how Ternary Operator works in JavaScriptLive Demo                    var a = 10;          var b = 20;          var linebreak = "";          document.write ("((a > b) ? 100 : 200) => ");          result = (a > b) ? 100 : 200;          document.write(result);          document.write(linebreak);          document.write ("((a < b) ? 100 : 200) => ");          result = (a < b) ? 100 : 200;          document.write(result);          document.write(linebreak);          

To pass a parameter to setTimeout() callback, use the following syntax −setTimeout(functionname, milliseconds, arg1, arg2, arg3...)The following are the parameters −function name − The function name for the function to be executed.milliseconds − The number of milliseconds.arg1, arg2, arg3 − These are the arguments passed to the function.ExampleYou can try to run the following code to pass a parameter to a setTimeout() callbackLive Demo           Submit                function timeFunction() {             setTimeout(function(){ alert("After 5 seconds!"); }, 5000);          }          Click the above button and wait for 5 seconds.    

To execute an anonymous function you need to use the leading bang! or any other symbol −!function(){    // do stuff }();You can also write it like −+function(){    // do stuff }();Even the following is an acceptable syntax −~function(){    // do stuff    return 0; }( );

To determine if an argument is sent to function, use “default” parameters.ExampleYou can try to run the following to implement itLive Demo                    function display(arg1 = 'Tutorials', arg2 = 'Learning') {             document.write(arg1 + ' ' +arg2+"");          }          display('Tutorials', 'Learning');          display('Tutorials');          display();          

To call multiple JavaScript functions in on click event, use a semicolon as shown below −onclick="Display1();Display2()"ExampleLive Demo                    function Display1() {             document.write ("Hello there!");          }          function Display2() {             document.write ("Hello World!");          }                     Click the following button to call the function