Javascript Var In Quotes

var person = {name: "John",                surname: "Smith",                address: {                  street: "13 Duncannon Street",                  city: "London",                  country: "United Kingdom"                }};

Function expressions and variables declared inside a function without using var become global properties.

If you assign a new variable without using the var keyword, that variable will be global, even if you are first assigning it in a function.

suppress empty strings in the output array when the separator is a regular expression: var f = '|a|b|c|'.split(/\|/); // f is ['a', 'b', 'c'] on some systems, and // f is ['', 'a', 'b', 'c', ''] on others string.substring(start, end ) The substring method is the same as the slice method except that it doesn’t handle the adjustment for negative parameters. There is no reason to use the substring method. Use slice instead. string.toLocaleLowerCase( ) The toLocaleLowerCase method produces a new string that is made by converting this string to lowercase using the rules for the locale. This is primarily for the benefit of Turkish because in that language `I’ converts to 1

var books = new Array(new Book(), new Book(), new Book());

The || operator can be used to fill in default values: var middle = stooge["middle-name"] || "(none)"; var status = flight.status || "unknown";

var wrapped = wrapElements([ 10, 20, 30, 40, 50]); var f = wrapped[ 0]; f();

With the handy map method of arrays (introduced in ES5), we can completely eliminate the loop details, implementing just the element-by-element transformation with a local function: Click here to view code image var names = [" Fred", "Wilma", "Pebbles"]; var upper = names.map( function( name) { return name.toUpperCase(); });

When used inside of a function, the var statement defines the function’s private variables.

Names A name is a letter optionally followed by one or more letters, digits, or underbars. A name cannot be one of these reserved words: abstract boolean break byte case catch char class const continue debugger default delete do double else enum export extends false final finally float for function goto if implements import in instanceof int interface long native new null package private protected public return short static super switch synchronized this throw throws transient true try typeof var volatile void while with Most of the reserved words in this list are not used in the language. The list does not include some words that should have been reserved but were not, such as undefined, NaN, and Infinity. It is not permitted to name a variable or parameter with a reserved word. Worse, it is not permitted to use a reserved word as the name of an object property in an object literal or following a dot in a refinement. Names are used for statements, variables, parameters, property names, operators, and labels.

abstract boolean break byte case catch char class const continue debugger default do else enum export extends false final finally float for function goto if implements import in instanceof int interface let long native new null package private protected public return short super switch synchronized this throws transient true try typeof var void volatile while with Comments

var -  used to declare variables with the option of initializing the variable to a value let – used for declaring local values with a block scope and the option of initializing the variable to a value const – used to declare read-only named constants with block scope.

function imgLoad(url) { return new Promise(function(resolve, reject) { var request = new XMLHttpRequest(); request.open('GET', url); request.responseType = 'blob'; request.onload = function() { if (request.status === 200) { resolve(request.response); } else { reject(Error('Image didn\'t load successfully; error code:' + request.statusText)); } }; request.onerror = function() { reject(Error('There was a network error.')); }; request.send(); }); }

function showHeroes(jsonObj) { var heroes = jsonObj['members']; for (var i = 0; i < heroes.length; i++) { var myArticle = document.createElement('article'); var myH2 = document.createElement('h2'); var myPara1 = document.createElement('p'); var myPara2 = document.createElement('p'); var myPara3 = document.createElement('p'); var myList = document.createElement('ul'); myH2.textContent = heroes[i].name; myPara1.textContent = 'Secret identity: ' + heroes[i].secretIdentity; myPara2.textContent = 'Age: ' + heroes[i].age; myPara3.textContent = 'Superpowers:'; var superPowers = heroes[i].powers; for (var j = 0; j < superPowers.length; j++) { var listItem = document.createElement('li'); listItem.textContent = superPowers[j]; myList.appendChild(listItem); } myArticle.appendChild(myH2); myArticle.appendChild(myPara1); myArticle.appendChild(myPara2); myArticle.appendChild(myPara3); myArticle.appendChild(myList); section.appendChild(myArticle); } }

// Arrays var trees = ['elm', 'ash', 'cedar', 'poplar', 'maple']; 0 in trees; // will return true 3 in trees; // will return true 6 in trees; // will return false 'ash' in trees;    // will return false (the index number must be specified,