{"id":707,"date":"2010-07-07T01:31:19","date_gmt":"2010-07-07T01:31:19","guid":{"rendered":"http:\/\/www.phpmind.com\/blog\/?p=707"},"modified":"2010-07-17T01:35:43","modified_gmt":"2010-07-17T01:35:43","slug":"javascript-variable-manipulation-functions","status":"publish","type":"post","link":"https:\/\/www.phpmind.com\/blog\/2010\/07\/javascript-variable-manipulation-functions\/","title":{"rendered":"JavaScript Refrence"},"content":{"rendered":"

JavaScript Variable Manipulation Functions<\/h2>\n

As shown in the following table, you can use these JavaScript statements in your own code to create and modify variables in your JavaScript functions.<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Element<\/th>\nDescription<\/th>\n<\/tr>\n
var myVar = 0;<\/span><\/td>\nCreates a variable with given starting value. Type is determined dynamically.<\/td>\n<\/tr>\n
stringVar = prompt(“message”)<\/span><\/td>\nSends message to user in a dialog <\/span>box<\/span><\/span><\/a>, retrieves text input from user and stores it in stringVar<\/span>.<\/td>\n<\/tr>\n
stringVar.length<\/span><\/td>\nReturns the length (in characters) of stringVar<\/span>.<\/td>\n<\/tr>\n
stringVar.toUpperCase(), stringVar.toLowerCase()<\/span><\/td>\nConverts stringVar<\/span> to upper- or lowercase.<\/td>\n<\/tr>\n
stringVar.substring()<\/span><\/td>\nReturns a specified subset of stringVar<\/span>.<\/td>\n<\/tr>\n
stringVar.indexOf()<\/span><\/td>\nReturns location of a substring in stringVar<\/span> (or -1<\/span>).<\/td>\n<\/tr>\n
parseInt()<\/span><\/td>\nConverts string<\/span> to int<\/span>.<\/td>\n<\/tr>\n
parseFloat()<\/span><\/td>\nConverts string<\/span> to float<\/span>.<\/td>\n<\/tr>\n
toString()<\/span><\/td>\nConverts any variable to string<\/span>.<\/td>\n<\/tr>\n
eval()<\/span><\/td>\nEvaluates string<\/span> as JavaScript code.<\/td>\n<\/tr>\n
Math.ceil()<\/span><\/td>\nConverts any number to integer by rounding up.<\/td>\n<\/tr>\n
Math.floor()<\/span><\/td>\nConverts any number to integer by rounding down.<\/td>\n<\/tr>\n
Math.round()<\/span><\/td>\nConverts any number to integer by standard rounding algorithm.<\/td>\n<\/tr>\n
Math.random()<\/span><\/td>\nReturns random float between 0 and 1.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n

Basic I\/O Commands in JavaScript<\/h2>\n

JavaScript programmers commonly use the commands shown in the following table for controlling dialog-based input and output in programs to be used on the Web.<\/p>\n\n\n\n\n\n
Element<\/th>\nDescription<\/th>\n<\/tr>\n
alert(“message”);<\/span><\/td>\nCreates a popup dialog containing “message.”<\/td>\n<\/tr>\n
stringVar = prompt(“message”)<\/span><\/td>\nSend message to user in a dialog box, retrieve text input from user and store it in stringVar<\/span>.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
\n

JavaScript Conditions and Branching Code Structures<\/h2>\n

Look to the following table for JavaScript control structures you can use in your program code to add branching and looping behavior to your JavaScript programs.<\/p>\n\n\n\n\n\n\n\n\n
Element<\/th>\nDescription<\/th>\n<\/tr>\n
if (condition){<\/span>
\n<\/span><\/p>\n

\/\/ content<\/span> <\/span><\/p>\n

} else {<\/span> <\/span><\/p>\n

\/\/ more content<\/span> <\/span><\/p>\n

} \/\/ end if<\/span><\/td>\n

Executes content only if condition is true.<\/p>\n

Optional else<\/span> clause occurs if condition
\nis false.<\/td>\n<\/tr>\n

switch (expression)<\/span> <\/span><\/p>\n

case: value;<\/span> <\/span><\/p>\n

\/\/code<\/span> <\/span><\/p>\n

break;<\/span><\/p>\n

default:<\/span><\/p>\n

\/\/code<\/span>
\n<\/span>}<\/span><\/td>\n

Compares expression against one or more values. If expression
\nis equal to value, runs corresponding code.<\/p>\n

Default clause catches any uncaught values.<\/td>\n<\/tr>\n

for(i = 0; i < count; i++)<\/span><\/p>\n

\/\/code<\/span><\/p>\n

} \/\/ end for<\/span><\/td>\n

Repeats code i<\/span> times.<\/td>\n<\/tr>\n
While (condition){<\/span><\/p>\n

\/\/code<\/span><\/p>\n

} \/\/ end while<\/span><\/td>\n

Repeats code as long as condition is true.<\/td>\n<\/tr>\n
Function fnName(paramaters) {<\/span><\/p>\n

\/\/code<\/span><\/p>\n

} \/\/ end function<\/span><\/td>\n

Defines a function named fnName<\/span> and
\nsends it parameters. All code inside the function will execute when
\nthe function is called.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
\n

Add JavaScript Comparison Operators to Condition Statements<\/h2>\n

JavaScript uses comparison operators inside conditions to make numeric or alphabetical comparisons of variables to other variables or values. Using these operators, you can determine whether a variable is greater than, less than, or equal to another variable or value. You can also use combinations of these comparison operators.<\/p>\n\n\n\n\n\n\n\n\n\n
Name<\/th>\nOperator<\/th>\nExample<\/th>\nNotes<\/th>\n<\/tr>\n
Equality<\/td>\n==<\/span><\/td>\n(x==3)<\/span><\/td>\nWorks with all variable types, including strings.<\/td>\n<\/tr>\n
Not equal<\/td>\n!=<\/span><\/td>\n(x != 3)<\/span><\/td>\nTrue if values are not equal.<\/td>\n<\/tr>\n
Less than<\/td>\n<<\/span><\/td>\n(x < 3)<\/span><\/td>\nNumeric or alphabetical comparison.<\/td>\n<\/tr>\n
Greater than<\/td>\n><\/span><\/td>\n(x > 3)<\/span><\/td>\nNumeric or alphabetical comparison.<\/td>\n<\/tr>\n
Less than or equal to<\/td>\n<=<\/span><\/td>\n(x <= 3)<\/span><\/td>\nNumeric or alphabetical comparison.<\/td>\n<\/tr>\n
Greater than or equal to<\/td>\n>=<\/span><\/td>\n(x >= 3)<\/span><\/td>\nNumeric or alphabetical comparison.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
\n

Create JavaScript Structures and Objects<\/h2>\n

JavaScript allows you to put together code lines to create functions and variables to create arrays. You can put functions and variables together to create objects.<\/p>\n\n\n\n\n\n\n\n
Element<\/strong><\/td>\nDescription<\/strong><\/td>\n<\/tr>\n
function fnName(parameters) {<\/span>
\n<\/span><\/p>\n

\/\/code<\/span> <\/span><\/p>\n

} \/\/ end function<\/span><\/td>\n

Defines a function named fnName<\/span> and
\nsends it parameters. All code inside function will execute when the
\nfunction is called.<\/td>\n<\/tr>\n
var myArray = new Array(“a”,
\n“b”, “c”);<\/span><\/td>\n		Creates an array. Elements can be any type (even mixed
\ntypes).<\/td>\n<\/tr>\n
Var myJSON = {<\/span> <\/span><\/p>\n

“name”:
\n“Andy”,<\/span> <\/span><\/p>\n

“title”:
\n“Author”<\/span> <\/span><\/p>\n

}<\/span><\/td>\n

Creates a JSON<\/span> object. Each element
\nhas a name\/value pair, and can contain anything, including an array
\n(with square braces) another JSON<\/span> object,
\nor a function.<\/td>\n<\/tr>\n
Var person = new Object();<\/span> <\/span><\/p>\n

Person.name =
\n“Andy”;<\/span><\/td>\n

Creates an object. You can add ordinary variables (which become
\nproperties) or functions (which become methods).<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
\n

Change Your Web Page with JavaScript Document Object Model Methods<\/h2>\n

The Document Object Model methods shown in the following table offer you a great way to access and modify your Web pages through your JavaScript code.<\/p>\n\n\n\n\n\n\n\n\n\n
Element<\/strong><\/td>\nDescription<\/strong><\/td>\n<\/tr>\n
myElement =
\ndocument.getElementById(“name”);<\/span><\/td>\n		Gets an element from the page with the specified ID and copies
\na reference to that element to the variable myElement<\/span>.<\/td>\n<\/tr>\n
myElement.innerHTML =
\n“value”<\/span><\/td>\n		Changes the value of the element to “value”<\/span>.<\/td>\n<\/tr>\n
document.onkeydown = keyListener<\/span><\/td>\nWhen a key is pressed, a function called keyListener<\/span> is automatically activated.<\/td>\n<\/tr>\n
document.onmousemove =
\nmouseListener<\/span><\/td>\n		When the mouse is moved, a function called mouseListener<\/span> is automatically activated.<\/td>\n<\/tr>\n
setInterval(function, ms);<\/span><\/td>\nRuns function each ms<\/span>
\nmilliseconds.<\/td>\n<\/tr>\n
myArray =
\ndocument.getElementByName(“name”)<\/span><\/td>\n		Returns an array of objects with the current name (frequently
\nused with radio buttons).<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

JavaScript Variable Manipulation Functions As shown in the following table, you can use these JavaScript statements in your own code to create and modify variables in your JavaScript functions. Element Description var myVar = 0; Creates a variable with given starting value. Type is determined dynamically. stringVar = prompt(“message”) Sends message to user in a […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"categories":[27],"tags":[],"class_list":["post-707","post","type-post","status-publish","format-standard","hentry","category-javascript"],"_links":{"self":[{"href":"https:\/\/www.phpmind.com\/blog\/wp-json\/wp\/v2\/posts\/707","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.phpmind.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.phpmind.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.phpmind.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.phpmind.com\/blog\/wp-json\/wp\/v2\/comments?post=707"}],"version-history":[{"count":14,"href":"https:\/\/www.phpmind.com\/blog\/wp-json\/wp\/v2\/posts\/707\/revisions"}],"predecessor-version":[{"id":831,"href":"https:\/\/www.phpmind.com\/blog\/wp-json\/wp\/v2\/posts\/707\/revisions\/831"}],"wp:attachment":[{"href":"https:\/\/www.phpmind.com\/blog\/wp-json\/wp\/v2\/media?parent=707"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.phpmind.com\/blog\/wp-json\/wp\/v2\/categories?post=707"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.phpmind.com\/blog\/wp-json\/wp\/v2\/tags?post=707"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}