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javascriptpromise
Iftikhar Ali
Iftikhar Ali

Reputation: 401

Returning promises from Synchronous JS Functions

I'm trying to understand promises in JavaScript.

For my example scenario, I want to write a method which either returns data from local "Cache" if available or makes an HTTP call to retrieve the data from server. I always want to return a promise even when no asynchronous calls was made so that user of my JS function has a unified API. How can I achieve that in Javascript. I'm in ES 5.

Upvotes: 0

Views: 52

Answers (2)

Yasin Yaqoobi
Yasin Yaqoobi

Reputation: 2040

First promises is ES-6/ecma2015 feature so you have to use something like babel https://babeljs.io/ or even better you can use this pollyfill https://github.com/getify/native-promise-only. 

var promise = getValue(); 
promise.then('do your stuff here '); 


function getValue(){
    return new Promise(function executor(resolve,error){ 
         getData(resolve);   // call your function that gets the data.
    }); 
}

Upvotes: 0

Kevin
Kevin

Reputation: 25269

You want them Promise.resolve function, which takes a value to be immediately resolved. Since you're on es5, you can either use a promise library like Bluebird, or you can use a transpiler like Babel to compile ES6 down to ES5.

Upvotes: 1

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