{"id":27695,"date":"2022-12-25T22:35:20","date_gmt":"2022-12-25T17:05:20","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-why-doesnt-promisify-want-the-argument-for-the-callback-function\/"},"modified":"2022-12-25T22:35:20","modified_gmt":"2022-12-25T17:05:20","slug":"solved-why-doesnt-promisify-want-the-argument-for-the-callback-function","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-why-doesnt-promisify-want-the-argument-for-the-callback-function\/","title":{"rendered":"[Solved] Why doesn’t promisify want the argument for the callback function?"},"content":{"rendered":"

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I mean opA<\/code> is a function, so why not opA()<\/code>?<\/p>\n<\/blockquote>\n

Because opA<\/code> is a reference to the function itself. The promise will use that reference to execute that function at a later time.<\/p>\n

Alternatively, opA()<\/code> executes the function (without any arguments) now<\/em> and passes the result<\/em> of that function call to the promise. Since your opA<\/code> function doesn’t return anything, it would pass undefined<\/code> to the promise. The promise would then have nothing to execute later after it completes its operation(s). The setTimeout<\/code> would then also fail because cb<\/code> is also undefined<\/code>, because no arguments were passed to opA()<\/code>.<\/p>\n

Any time you do see a structure like that, either (1) it’s a bug or (2) the function intentionally builds and returns a callback function intended for the promise. For example, if you write a function which returns<\/em> opA<\/code> then you can invoke that function and pass its result to promisify<\/code>.<\/p>\n

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An important clue to this behavior is here:<\/p>\n

const opA = ...\n<\/code><\/pre>\n
opA<\/code> is a variable, not unlike any other variable.  It contains a value or a reference to something.  In this case it’s a reference to a function.  You could re-assign that variable, pass it as a function argument, set it as a property on an object, etc. just like any other.<\/p>\n<\/p><\/div>\n
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solved Why doesn’t promisify want the argument for the callback function? <\/p>\n","protected":false},"excerpt":{"rendered":"
[ad_1] I mean opA is a function, so why not opA()? Because opA is a reference to the function itself. The promise will use that reference to execute that function at a later time. Alternatively, opA() executes the function (without any arguments) now and passes the result of that function call to the promise. Since … 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":[1144,898,333,902],"class_list":["post-27695","post","type-post","status-publish","format-standard","hentry","category-solved","tag-async-await","tag-ecmascript-6","tag-javascript","tag-node-js"],"yoast_head":"\n[Solved] Why doesn't promisify want the argument for the callback function? - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-why-doesnt-promisify-want-the-argument-for-the-callback-function\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] Why doesn't promisify want the argument for the callback function? - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] I mean opA is a function, so why not opA()? Because opA is a reference to the function itself. The promise will use that reference to execute that function at a later time. Alternatively, opA() executes the function (without any arguments) now and passes the result of that function call to the promise. Since ... 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