Created
March 10, 2018 06:32
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| const util = require('util'); | |
| const process = require('process'); | |
| const sleep = util.promisify(setTimeout); | |
| var a = function(callback){ | |
| callback(); | |
| } | |
| a(async function(){ | |
| console.log("print me first"); | |
| await sleep(2000); | |
| console.log("print me in last"); | |
| }) | |
| //queue callback for execution after given duration | |
| //so the given callback will be executed after all functions and event handlers already queued at that time. | |
| setTimeout( function(){ | |
| console.log("print me after 2000 ms"); | |
| },2000) | |
| //after currently executing I/O call back | |
| //similar to setTimeout(callback,0) but it doesn't check queue of functions but only the queue of I/O eventhandlers | |
| //Use setImmediate if you want to queue the function behind whatever I/O event callbacks that are already in the event queue. | |
| setImmediate( function(){ | |
| console.log("then me on 3rd priority"); | |
| }) | |
| const timeid= setInterval(function(){ | |
| console.log("then me on 2nd priority"); | |
| clearInterval(timeid); | |
| }, 0); | |
| //execute given callback once all the queued functions and event handlers are executed | |
| setTimeout( function(){ | |
| console.log("then me on 2nd priority too"); | |
| },0) | |
| //Use process.nextTick to effectively queue the function at the head of the event queue so that it executes immediately after the current function completes. | |
| process.nextTick( function(){//blocking | |
| console.log("then me on 1st priority"); | |
| }) | |
| //So in a case where you're trying to break up a long running, CPU-bound job using recursion, you would now want to use setImmediate rather than process.nextTick to queue the next iteration as otherwise any I/O event callbacks wouldn't get the chance to run between iterations. | |
| a(async function(){ | |
| console.log("print me first too"); | |
| await sleep(2000); | |
| console.log("print me in last too"); | |
| }) | |
| console.log("print me 2nd"); | |
| /* Output | |
| print me first | |
| print me first too | |
| print me 2nd | |
| then me on 1st priority | |
| then me on 2nd priority | |
| then me on 2nd priority too | |
| then me on 3rd priority | |
| print me after 2000 ms | |
| print me in last | |
| print me in last too | |
| */ |
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