{"id":1131,"date":"2016-12-19T10:45:56","date_gmt":"2016-12-19T01:45:56","guid":{"rendered":"http:\/\/belliny.net\/?p=1131"},"modified":"2016-12-19T10:45:56","modified_gmt":"2016-12-19T01:45:56","slug":"node-js-custom-callback-function-declare","status":"publish","type":"post","link":"https:\/\/www.belliny.net\/?p=1131","title":{"rendered":"Node.JS custom Callback function declare"},"content":{"rendered":"

http:\/\/stackoverflow.com\/questions\/2190850\/create-a-custom-callback-in-javascript<\/p>\n\n\n\n
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421<\/span>down vote<\/a>accepted<\/span><\/div>\n<\/td>\n
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Actually, your code will pretty much work as is, just declare your callback as an argument and you can call it directly using the argument name.<\/p>\n

The basics<\/h3>\n
function<\/span> doSomething<\/span>(<\/span>callback<\/span>)<\/span> {<\/span>\n    \/\/ ...<\/span>\n\n    \/\/ Call the callback<\/span>\n    callback<\/span>(<\/span>'stuff'<\/span>,<\/span> 'goes'<\/span>,<\/span> 'here'<\/span>);<\/span>\n}<\/span>\n\nfunction<\/span> foo<\/span>(<\/span>a<\/span>,<\/span> b<\/span>,<\/span> c<\/span>)<\/span> {<\/span>\n    \/\/ I'm the callback<\/span>\n    alert<\/span>(<\/span>a <\/span>+<\/span> \" \"<\/span> +<\/span> b <\/span>+<\/span> \" \"<\/span> +<\/span> c<\/span>);<\/span>\n}<\/span>\n\ndoSomething<\/span>(<\/span>foo<\/span>);<\/span><\/code><\/pre>\n
That will call\u00a0doSomething<\/code>, which will call\u00a0foo<\/code>, which will alert “stuff goes here”.<\/p>\n
Note that it’s very important to pass the function\u00a0reference<\/em>\u00a0(foo<\/code>), rather than calling the function and passing its result (foo()<\/code>). In your question, you do it properly, but it’s just worth pointing out because it’s a common error.<\/p>\n
More advanced stuff<\/h3>\n
Sometimes you want to call the callback so it sees a specific value for\u00a0this<\/code>. You can easily do that with the JavaScript\u00a0call<\/code>\u00a0function:<\/p>\n
function<\/span> Thing<\/span>(<\/span>name<\/span>)<\/span> {<\/span>\n    this<\/span>.<\/span>name <\/span>=<\/span> name<\/span>;<\/span>\n}<\/span>\nThing<\/span>.<\/span>prototype<\/span>.<\/span>doSomething <\/span>=<\/span> function<\/span>(<\/span>callback<\/span>)<\/span> {<\/span>\n    \/\/ Call our callback, but using our own instance as the context<\/span>\n    callback<\/span>.<\/span>call<\/span>(<\/span>this<\/span>);<\/span>\n}<\/span>\n\nfunction<\/span> foo<\/span>()<\/span> {<\/span>\n    alert<\/span>(<\/span>this<\/span>.<\/span>name<\/span>);<\/span>\n}<\/span>\n\nvar<\/span> t <\/span>=<\/span> new<\/span> Thing<\/span>(<\/span>'Joe'<\/span>);<\/span>\nt<\/span>.<\/span>doSomething<\/span>(<\/span>foo<\/span>);<\/span>  \/\/ Alerts \"Joe\" via `foo`<\/span><\/code><\/pre>\n
You can also pass arguments:<\/p>\n
function<\/span> Thing<\/span>(<\/span>name<\/span>)<\/span> {<\/span>\n    this<\/span>.<\/span>name <\/span>=<\/span> name<\/span>;<\/span>\n}<\/span>\nThing<\/span>.<\/span>prototype<\/span>.<\/span>doSomething <\/span>=<\/span> function<\/span>(<\/span>callback<\/span>,<\/span> salutation<\/span>)<\/span> {<\/span>\n    \/\/ Call our callback, but using our own instance as the context<\/span>\n    callback<\/span>.<\/span>call<\/span>(<\/span>this<\/span>,<\/span> salutation<\/span>);<\/span>\n}<\/span>\n\nfunction<\/span> foo<\/span>(<\/span>salutation<\/span>)<\/span> {<\/span>\n    alert<\/span>(<\/span>salutation <\/span>+<\/span> \" \"<\/span> +<\/span> this<\/span>.<\/span>name<\/span>);<\/span>\n}<\/span>\n\nvar<\/span> t <\/span>=<\/span> new<\/span> Thing<\/span>(<\/span>'Joe'<\/span>);<\/span>\nt<\/span>.<\/span>doSomething<\/span>(<\/span>foo<\/span>,<\/span> 'Hi'<\/span>);<\/span>  \/\/ Alerts \"Hi Joe\" via `foo`<\/span><\/code><\/pre>\n
Sometimes it’s useful to pass the arguments you want to give the callback as an array, rather than individually. You can use\u00a0apply<\/code>\u00a0to do that:<\/p>\n
function<\/span> Thing<\/span>(<\/span>name<\/span>)<\/span> {<\/span>\n    this<\/span>.<\/span>name <\/span>=<\/span> name<\/span>;<\/span>\n}<\/span>\nThing<\/span>.<\/span>prototype<\/span>.<\/span>doSomething <\/span>=<\/span> function<\/span>(<\/span>callback<\/span>)<\/span> {<\/span>\n    \/\/ Call our callback, but using our own instance as the context<\/span>\n    callback<\/span>.<\/span>apply<\/span>(<\/span>this<\/span>,<\/span> [<\/span>'Hi'<\/span>,<\/span> 3<\/span>,<\/span> 2<\/span>,<\/span> 1<\/span>]);<\/span>\n}<\/span>\n\nfunction<\/span> foo<\/span>(<\/span>salutation<\/span>,<\/span> three<\/span>,<\/span> two<\/span>,<\/span> one<\/span>)<\/span> {<\/span>\n    alert<\/span>(<\/span>salutation <\/span>+<\/span> \" \"<\/span> +<\/span> this<\/span>.<\/span>name <\/span>+<\/span> \" - \"<\/span> +<\/span> three <\/span>+<\/span> \" \"<\/span> +<\/span> two <\/span>+<\/span> \" \"<\/span> +<\/span> one<\/span>);<\/span>\n}<\/span>\n\nvar<\/span> t <\/span>=<\/span> new<\/span> Thing<\/span>(<\/span>'Joe'<\/span>);<\/span>\nt<\/span>.<\/span>doSomething<\/span>(<\/span>foo<\/span>);<\/span>  \/\/ Alerts \"Hi Joe - 3 2 1\" via `foo`<\/span><\/code><\/pre>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n\n\n
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down vote<\/a><\/div>\n<\/td>\n
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It is good practice to make sure the callback is an actual function before attempting to execute it:<\/p>\n
if<\/span> (<\/span>callback <\/span>&&<\/span> typeof<\/span>(<\/span>callback<\/span>)<\/span> ===<\/span> \"function\"<\/span>)<\/span> {<\/span>\n\n  callback<\/span>();<\/span>\n}<\/span><\/code><\/pre>\n
 <\/p>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
My 2 cent. Same but different…<\/p>\n
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<script><\/span>\n    dosomething<\/span>(<\/span>\"blaha\"<\/span>,<\/span> function<\/span>(){<\/span>\n        alert<\/span>(<\/span>\"Yay just like jQuery callbacks!\"<\/span>);<\/span>\n    });<\/span>\n\n\n    function<\/span> dosomething<\/span>(<\/span>damsg<\/span>,<\/span> callback<\/span>){<\/span>\n        alert<\/span>(<\/span>damsg<\/span>);<\/span>\n        if<\/span>(<\/span>typeof<\/span> callback <\/span>==<\/span> \"function\"<\/span>)<\/span> \n        callback<\/span>();<\/span>\n    }<\/span>\n<\/script><\/span><\/code><\/pre>\n<\/div>\n","protected":false},"excerpt":{"rendered":"
http:\/\/stackoverflow.com\/questions\/2190850\/create-a-custom-callback-in-javascript 421down voteaccepted Actually, your code will pretty much work as is, just declare your callback as an argument and you can call it directly using the argument name. The basics function doSomething(callback) { \/\/ … \/\/ Call the callback callback(‘stuff’, ‘goes’, ‘here’); } function foo(a, b, c) { \/\/ I’m the callback alert(a + … Continue reading “Node.JS custom Callback function declare”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[10],"tags":[],"class_list":["post-1131","post","type-post","status-publish","format-standard","hentry","category-node-js"],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.belliny.net\/index.php?rest_route=\/wp\/v2\/posts\/1131","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.belliny.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.belliny.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.belliny.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.belliny.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1131"}],"version-history":[{"count":0,"href":"https:\/\/www.belliny.net\/index.php?rest_route=\/wp\/v2\/posts\/1131\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.belliny.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1131"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.belliny.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1131"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.belliny.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1131"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}