You can also declare multiple variables at once in the same statement: var a = 1, b = 2
You can redeclare the variable many times, overriding it: var a = 1 If you don’t initialize the variable when you declare it, it will have the undefined value until you assign a value to it. In older environments (or with strict mode disabled) this will initialize the variable and assign it to the global object. In modern environments, with strict mode enabled, you will get an error. If you forget to add var you will be assigning a value to an undeclared variable, and the results might vary. Until ES2015, var was the only construct available for defining variables. Let’s dive into the specific features added to JavaScript since ES5. Why does this happen? During the process that led to ES2015, the name was changed from ES6 to ES2015, but since this was done late, people still referenced it as ES6, and the community has not left the edition naming behind - the world is still calling ES releases by edition number.
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So ES5 is the official name for the ECMAScript specification update published in 2009. I found it puzzling why sometimes an ES version is referenced by edition number and sometimes by year, and I am confused by the year by chance being -1 on the number, which adds to the general confusion around JS/ES ?īefore ES2015, ECMAScript specifications were commonly called by their edition. The members of TC39 are companies involved in JavaScript and browser vendors, including Mozilla, Google, Facebook, Apple, Microsoft, Intel, PayPal, SalesForce and others.Įvery standard version proposal must go through various stages, which are explained here. TC39 is the committee that evolves JavaScript. The current ECMAScript version is ES2018. So as of 201x, the only popular language supporting the ECMAScript spec is JavaScript. This press release by Netscape and Sun Microsystems (the maker of Java) might help figure out the name choice, which might include legal and branding issues by Microsoft which was in the committee, according to Wikipedia.Īfter IE9, Microsoft stopped branding its ES support in browsers as JScript and started calling it JavaScript (at least, I could not find references to it any more). When JavaScript was created, it was presented by Netscape and Sun Microsystems to Ecma and they gave it the name ECMA-262 alias ECMAScript. Why this weird name? Ecma International is a Swiss standards association who is in charge of defining international standards.
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Keeping up with the changes shouldn’t be harder than it already is, and my goal here is to give you a quick yet comprehensive overview of the new stuff available to us.Ĭlick here to get a PDF / ePub / Mobi version of this post to read offline Introduction to ECMAScript The future of JavaScript is going to be brilliant. JavaScript today is in the privileged position to be the only language that can run natively in the browser, and is highly integrated and optimized for that. I wrote this article to help you move from pre-ES6 knowledge of JavaScript and get you quickly up to speed with the most recent advancements of the language.
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