Try the event loop code for yourself and see how modifying the loop timing or moving items around affects the output to console.
run node ordered.js to run the eventloop in order file.
run node random.js to run the eventloop out of order file.
Created
December 17, 2021 06:07
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Node JS Event Loop
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| const fs = require('fs'); | |
| // Mainline | |
| console.log('Hello, ----------- mainline'); | |
| console.log('world. ----------- mainline'); | |
| // end mainline / pre timers phase 1 | |
| process.nextTick(() => { | |
| console.log('nexttick --------- before event loop'); | |
| }); | |
| // timers phase 1 | |
| setTimeout(() => { | |
| console.log('timeout - 0s ----- Timers 1'); | |
| }, 0); | |
| // timers phase 1 | |
| setImmediate(() => { | |
| console.log('immediate -------- Timers 1'); | |
| }); | |
| // timers phase 1 | |
| setTimeout(() => { | |
| console.log('timeout - 0s ----- Timers 1'); | |
| }, 0); | |
| // begin polling phase | |
| fs.readFile(__filename, () => { | |
| // end poll phase | |
| process.nextTick(() => { | |
| console.log('nexttick i/o ----- After Polling'); | |
| }); | |
| // check phase | |
| setImmediate(() => { | |
| console.log('immediate i/o ---- Check'); | |
| }); | |
| // timers phase 2 | |
| setTimeout(() => { | |
| console.log('timeout i/0 0s --- Timers 2'); | |
| }, 0); | |
| // timers phase 3 | |
| setTimeout(() => { | |
| console.log('timeout i/0 3s --- Timers 3'); | |
| }, 3000); | |
| }); | |
| // timers phase 4 | |
| setTimeout(() => { | |
| console.log('timeout - 5s ----- Timers 4'); | |
| }, 5000); | |
| process.on('beforeExit', () => { | |
| console.log('process.on ------- beforeExit'); | |
| }); |
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| const fs = require('fs'); | |
| // // blocking loop 2B | |
| // for (let i = 0; i < 2000000000; i++) { | |
| // if (i === 1999999999) { | |
| // console.log('blocking loop'); | |
| // } | |
| // } | |
| // timers phase 4 | |
| setTimeout(() => { | |
| console.log('timeout - 5s ----- Timers 4'); | |
| }, 5000); | |
| // Mainline | |
| console.log('Hello, ----------- mainline'); | |
| // timers phase 1 | |
| setTimeout(() => { | |
| console.log('timeout - 0s ----- Timers 1'); | |
| }, 0); | |
| // Before Exit | |
| process.on('beforeExit', () => { | |
| console.log('process.on ------- beforeExit'); | |
| }); | |
| // timers phase 1 | |
| setImmediate(() => { | |
| console.log('immediate -------- Timers 1'); | |
| }); | |
| // begin polling phase | |
| fs.readFile(__filename, () => { | |
| // timers phase 3 | |
| setTimeout(() => { | |
| console.log('timeout i/0 3s --- Timers 3'); | |
| // blocking loop 3B | |
| for (let i = 0; i < 3000000000; i++) { | |
| if (i === 2999999999) { | |
| console.log('blocking loop'); | |
| } | |
| } | |
| }, 3000); | |
| // check phase | |
| setImmediate(() => { | |
| console.log('immediate i/o ---- Check'); | |
| }); | |
| // timers phase 2 | |
| setTimeout(() => { | |
| console.log('timeout i/0 0s --- Timers 2'); | |
| }, 0); | |
| // end poll phase | |
| process.nextTick(() => { | |
| console.log('nexttick i/o ----- After Polling'); | |
| }); | |
| }); | |
| // end mainline / pre timers phase 1 | |
| process.nextTick(() => { | |
| console.log('nexttick --------- before event loop'); | |
| }); | |
| console.log('world. ----------- mainline'); | |
| // timers phase 1 | |
| setTimeout(() => { | |
| console.log('timeout - 0s ----- Timers 1'); | |
| }, 0); |
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