{"id":19548,"date":"2022-11-07T01:43:54","date_gmt":"2022-11-06T20:13:54","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-what-is-this-form-or-syntax-called-in-javascript-closed\/"},"modified":"2022-11-07T01:43:54","modified_gmt":"2022-11-06T20:13:54","slug":"solved-what-is-this-form-or-syntax-called-in-javascript-closed","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-what-is-this-form-or-syntax-called-in-javascript-closed\/","title":{"rendered":"[Solved] What is this form or syntax called in javascript? [closed]"},"content":{"rendered":"

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How can the variable name<\/code> be redefined?<\/p>\n<\/blockquote>\n

It isn’t.<\/p>\n

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What’s with the left to right assignment? Doesn’t = work right to left?<\/p>\n<\/blockquote>\n

Yes, and that’s what’s happening here. That’s destructuring assignment<\/a>. This one line:<\/p>\n

const {key1: value1, key2:value2} = name\n<\/code><\/pre>\n
is the equivalent of this:<\/p>\n
const value1 = name.key1;\nconst value2 = name.key2;\n<\/code><\/pre>\n
You’re quite right that it looks like an object being assigned to a variable, but in reverse. That’s intentional. When you do:<\/p>\n
const x = {a: 1, b: 2};\n<\/code><\/pre>\n
you’re creating an object (putting together a structure) and assigning it to x<\/code>. When you do:<\/p>\n
const {a: vara, b: varb} = x;\n<\/code><\/pre>\n
you’re destructuring<\/em> (taking a structure apart) the object on the right into the targets (vara<\/code> and varb<\/code>) on the left. The syntax for this is identical<\/strong>, just reversed. Both forms also have a shorthand version:<\/p>\n
const a = 1;\nconst b = 2;\nconst x = {a, b};\n<\/code><\/pre>\n
creates an object with a<\/code> and b<\/code> properties (with the values from the a<\/code> and b<\/code> in-scope identifiers). This;<\/p>\n
const {a, b} = x;\n<\/code><\/pre>\n
takes a<\/code> and b<\/code> properties from x<\/code> and uses it to set the value of the constants a<\/code> and b<\/code>.<\/p>\n
I should note that nothing about destructuring is tied to let<\/code> or const<\/code> (or var<\/code>). Just like you can use any in-scope variable or a property to provide the value for an object property when creating an object, you can do the same when destructuring. Because object destructuring starts with {<\/code>, if you’re not doing it in an expression you need to put a (<\/code> in front of it so the {<\/code> doesn’t look like the beginning of a block:<\/p>\n<\/p>\n
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const x = {a: 1, b: 2};\r\nlet a, b;\r\n\r\n({a, b} = x);\r\nconsole.log(a, b); \/\/ 1 2\r\n\r\nconst y = {};\r\n\r\n({a: y.ayyy, b: y.beee} = x);\r\nconsole.log(y); \/\/ {ayyy: 1, beee: 2}<\/code><\/pre>\n<\/div>\n<\/div>\n
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what name<\/code> is referenced in the line marked ***? The one initially passed or the object created?<\/p>\n<\/blockquote>\n
There is no object created in that code. (Well, the arrow function is an object, and there are behind-the-scenes specification-level objects like the lexical environment, but…)<\/p>\n
It’s impossible to say what name<\/code> is in the line you’ve marked because that’s a syntax error, the function<\/code> keyword starts a function declaration that’s never finished. If by function(name)<\/code> you meant someFunction(name)<\/code>, it would be the name<\/code> passed into the arrow function.<\/p>\n<\/p><\/div>\n
<\/div>\n<\/div>\n
            0<\/span> <\/p><\/div>\n<\/div>\n
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solved What is this form or syntax called in javascript? [closed] <\/p>\n","protected":false},"excerpt":{"rendered":"
[ad_1] How can the variable name be redefined? It isn’t. What’s with the left to right assignment? Doesn’t = work right to left? Yes, and that’s what’s happening here. That’s destructuring assignment. This one line: const {key1: value1, key2:value2} = name is the equivalent of this: const value1 = name.key1; const value2 = name.key2; You’re … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[333,902],"class_list":["post-19548","post","type-post","status-publish","format-standard","hentry","category-solved","tag-javascript","tag-node-js"],"yoast_head":"\n[Solved] What is this form or syntax called in javascript? 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