Gurukula

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eventloop_async_blocking.js 
fastify.get('/async-block-event-loop', async (_request, reply) => {
  const hash = crypto.createHash('sha256');
  const numberOfHasUpdates = 10e6;

  const updatehashAsync = async () => {
    hash.update(randomString());
  };

  for (let iter = 0; iter < numberOfHasUpdates; iter++) {
    await updatehashAsync();
  }
  reply.send({ data: 'Finished long process' });
});
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eventloop_unblocking_event_loop.js 
fastify.get('/unblock-event-loop', async (_request, reply) => {
  const hash = crypto.createHash('sha256');
  const numberOfHasUpdates = 10e6;

  const breathSpace = async delayInS =>
    new Promise(res => setTimeout(() => res(), delayInS * 1000));

  for (let iter = 0; iter < numberOfHasUpdates; iter++) {
    await hash.update(getRandomString());
    await breathSpace(0);
  }
  reply.send({ data: 'Finished long process' });
});
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macro_and_micro_tasks.js 
function logA() { console.log('A') };
function logB() { console.log('B') };
function logC() { console.log('C') };
function logD() { console.log('D') };
function logE() { console.log('E') };
function logF() { console.log('F') };
function logG() { console.log('G') };
function logH() { console.log('H') };
function logI() { console.log('I') };
function logJ() { console.log('J') };

logA();
setTimeout(logG, 0);
Promise.resolve()
  .then(logC)
  .then(setTimeout(logH))
  .then(logD)
  .then(logE)
  .then(logF);
setTimeout(logI);
setTimeout(logJ);
logB();
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macro_and_micro_tasks.js 
function logA() { console.log('A') };
function logB() { console.log('B') };
function logC() { console.log('C') };
function logD() { console.log('D') };
function logE() { console.log('E') };
function logF() { console.log('F') };
function logG() { console.log('G') };
function logH() { console.log('H') };
function logI() { console.log('I') };
function logJ() { console.log('J') };

logA();
setTimeout(logG, 0);
Promise.resolve()
  .then(logC)
  .then(setTimeout(logH))
  .then(logD)
  .then(logE)
  .then(logF);
setTimeout(logI);
setTimeout(logJ);
logB();
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racer.js 
setTimeout(() => console.log('timeout'), 0);
setImmediate(() => console.log('immediate'));
process.nextTick(() => console.log('nextTick'));
console.log('current event loop');
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process.tick over setImmediate 
setImmediate(() => console.log('I run immediately'))
process.nextTick(() => console.log('But I run before that'))
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process.tick starving others 
let count = 0
const cb = () => {
    console.log(`Processing nextTick cb ${++count}`)
    process.nextTick(cb)
}
setImmediate(() => console.log('setImmediate is called'))
setTimeout(() => console.log('setTimeout executed'), 100)
process.nextTick(cb)
console.log('Start')
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Good fellow setImmediate 
let count = 0
const cb = () => {
    console.log(`Processing setImmediate cb ${++count}`)
    setImmediate(cb)
}
setImmediate(cb)
setTimeout(() => console.log('setTimeout executed'), 100)
console.log('Start')
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setTimeout issue 
console.log('Foo: Start', new Date().toLocaleTimeString());

setTimeout(() => {
  console.log(
    'Poo: To be called in 5 seconds ',
    new Date().toLocaleTimeString()
  );
}, 5000);

const waitlogForNseconds = seconds => {
  const startTime = new Date().getTime();
  const milliseconds = 1000;
  const endTime = startTime + seconds * milliseconds;
  let currTime = new Date().getTime();
  while (endTime > currTime) {
    currTime = new Date().getTime();
  }
  console.log(
    `Goo: To be called after ${seconds} End `,
    new Date().toLocaleTimeString()
  );
};

waitlogForNseconds(10);

console.log('Bar: ', new Date().toLocaleTimeString());
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setTimeout issue 
console.log('Foo: Start', new Date().toLocaleTimeString());

setTimeout(() => {
  console.log(
    'Poo: To be called in 5 seconds ',
    new Date().toLocaleTimeString()
  );
}, 5000);

const waitlogForNseconds = seconds => {
  const startTime = new Date().getTime();
  const milliseconds = 1000;
  const endTime = startTime + seconds * milliseconds;
  let currTime = new Date().getTime();
  while (endTime > currTime) {
    currTime = new Date().getTime();
  }
  console.log(
    `Goo: To be called after ${seconds} End `,
    new Date().toLocaleTimeString()
  );
};

waitlogForNseconds(10);

console.log('Bar: ', new Date().toLocaleTimeString());
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Non Pure function 
const assert = require('assert');

const configs = {
  YEARLY_INTEREST_RATE: 4.0
};

const getSavingsAmount = amount => {
  return amount + amount * (configs.YEARLY_INTEREST_RATE / 100);
};

assert(getSavingsAmount(100) === 104);

configs.YEARLY_INTEREST_RATE = 3.0;

assert(getSavingsAmount(100) === 104);
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Pure function 
const assert = require('assert');

const getSavingsAmount = (amount, interestRate) => {
  return amount + amount * (interestRate / 100);
};

assert(getSavingsAmount(100, 3) === 103);
assert(getSavingsAmount(100, 2) === 102);
assert(getSavingsAmount(100, 4) === 104); 
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mutating function side affects 
const foo = {
  'ONE':1,
  'TWO':2
};

const mapMultiplier = (params, multiplier) => {
  params.ONE = params.ONE * multiplier
  params.TWO = params.TWO * multiplier
  return params;
};

console.log(mapMultiplier(foo, 2));
console.log(mapMultiplier(foo, 3));
console.log(mapMultiplier(foo, 4));

// Value of foo { 'ONE': 1, 'TWO': 2 }
console.log('foo: ', foo);
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non mutating function, no side affects 
const foo = {
  ONE: 1,
  TWO: 2
};
const mapMultiplier = (params, multiplier) => {
  // Only shallow clone works, deep clone is expensive and need other mechanisms
  const paramsCopy = { ...params }; // Object.freeze(params); //  Object.assign({}, params)
  paramsCopy.ONE = paramsCopy.ONE * multiplier;
  paramsCopy.TWO = paramsCopy.TWO * multiplier;
  return paramsCopy;
};
console.log(mapMultiplier(foo, 2));
console.log(mapMultiplier(foo, 3));
console.log(mapMultiplier(foo, 4));

// Value of foo { 'ONE': 1, 'TWO': 2 }
console.log('foo: ', foo);
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Immutable examples 
/******** Array  ********/

// Instead of simple assigment
const a = Object.freeze([4, 5, 6]);
const b = [...[4, 5, 6]];

// Instead of: a.push(7, 8, 9);
const b = a.concat(7, 8, 9);
const c = [...a, 3]

// Instead of: a.pop();
const c = a.slice(0, -1);

// Instead of: a.unshift(1, 2, 3);
const d = [1, 2, 3].concat(a);

// Instead of: a.shift();
const e = a.slice(1);

/******** Maps ********/
const map = new Map([
  [1, 'one'],
  [2, 'two'],
  [3, 'three']
]);

// Instead of: map.set(4, 'four');
const map2 = new Map([...map, [4, 'four']]);

// Instead of: map.delete(1);
const map3 = new Map([...map].filter(([key]) => key !== 1));

// Instead of: map.clear();
const map4 = new Map();

/******** Sets ********/

const set = new Set(['A', 'B', 'C']);

// Instead of: set.add('D');
const set2 = new Set([...set, 'D']);

// Instead of: set.delete('B');
const set3 = new Set([...set].filter(key => key !== 'B'));

// Instead of: set.clear();
const set4 = new Set();
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Immutable examples 
/******** Array  ********/

// Instead of simple assigment
const a = Object.freeze([4, 5, 6]);
const b = [...[4, 5, 6]];

// Instead of: a.push(7, 8, 9);
const b = a.concat(7, 8, 9);
const c = [...a, 3]

// Instead of: a.pop();
const c = a.slice(0, -1);

// Instead of: a.unshift(1, 2, 3);
const d = [1, 2, 3].concat(a);

// Instead of: a.shift();
const e = a.slice(1);

/******** Maps ********/
const map = new Map([
  [1, 'one'],
  [2, 'two'],
  [3, 'three']
]);

// Instead of: map.set(4, 'four');
const map2 = new Map([...map, [4, 'four']]);

// Instead of: map.delete(1);
const map3 = new Map([...map].filter(([key]) => key !== 1));

// Instead of: map.clear();
const map4 = new Map();

/******** Sets ********/

const set = new Set(['A', 'B', 'C']);

// Instead of: set.add('D');
const set2 = new Set([...set, 'D']);

// Instead of: set.delete('B');
const set3 = new Set([...set].filter(key => key !== 'B'));

// Instead of: set.clear();
const set4 = new Set();
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Immutable examples 
/******** Array  ********/

// Instead of simple assigment
const a = Object.freeze([4, 5, 6]);
const b = [...[4, 5, 6]];

// Instead of: a.push(7, 8, 9);
const b = a.concat(7, 8, 9);
const c = [...a, 3]

// Instead of: a.pop();
const c = a.slice(0, -1);

// Instead of: a.unshift(1, 2, 3);
const d = [1, 2, 3].concat(a);

// Instead of: a.shift();
const e = a.slice(1);

/******** Maps ********/
const map = new Map([
  [1, 'one'],
  [2, 'two'],
  [3, 'three']
]);

// Instead of: map.set(4, 'four');
const map2 = new Map([...map, [4, 'four']]);

// Instead of: map.delete(1);
const map3 = new Map([...map].filter(([key]) => key !== 1));

// Instead of: map.clear();
const map4 = new Map();

/******** Sets ********/

const set = new Set(['A', 'B', 'C']);

// Instead of: set.add('D');
const set2 = new Set([...set, 'D']);

// Instead of: set.delete('B');
const set3 = new Set([...set].filter(key => key !== 'B'));

// Instead of: set.clear();
const set4 = new Set();
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Higher order functions 
const withLog = (fn) => {  
  return (...args) => {  
	console.log(`calling ${fn.name}`);  
	return fn(...args);  
  };  
};
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Higher order functions 
const withLog = (fn) => {  
  return (...args) => {  
	console.log(`calling ${fn.name}`);  
	return fn(...args);  
  };  
};
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Higher order functions 
const withLog = (fn) => {  
  return (...args) => {  
	console.log(`calling ${fn.name}`);  
	return fn(...args);  
  };  
};
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Higher order functions 
const withLog = (fn) => {  
  return (...args) => {  
	console.log(`calling ${fn.name}`);  
	return fn(...args);  
  };  
};
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Higher order functions 
const withLog = (fn) => {  
  return (...args) => {  
	console.log(`calling ${fn.name}`);  
	return fn(...args);  
  };  
};
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Test pure functions 
const assert = require('assert');

const add = (a, b) => a + b;

assert(add(2, 3) === 5);
assert(add(2, 3) <= 6);
assert(add(2, 3) != 10);
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composition example 
const getSimpleText = text => {
  return text.toString().toLowerCase();
};

const getCurrentDateTime = () => new Date().toISOString();

const loggerWithTimeStamp = text => getCurrentDateTime() + ':  ' + getSimpleText(text);

const loggerWithTimeStampAndLevel = (text, level) => ` [ ${level.toUpperCase()} ] ${loggerWithTimeStamp(text)}`;

const loggerWithTimeStampAndLevelAndCallee = (text, level, callee) => {
  return 'Task: ' + callee + loggerWithTimeStampAndLevel(text, level);
};

const log = function(text, level) {
  if (level) {
    console[level](
      loggerWithTimeStampAndLevelAndCallee(text, level, log.caller.name)
    );
  } else {
    console.info(
      loggerWithTimeStampAndLevelAndCallee(text, 'info', log.caller.name)
    );
  }
};

(function run() {
  log('This is logger statement');
  log(Buffer.from('Something to log'), 'warn');
  log('This is logger statement', 'error');
  log('This is logger statement', 'error');
  log('This is logger statement', 'error');
})();
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Pure function 
const assert = require('assert');

const getSavingsAmount = (amount, interestRate) => {
  return amount + amount * (interestRate / 100);
};

assert(getSavingsAmount(100, 3) === 103);
assert(getSavingsAmount(100, 2) === 102);
assert(getSavingsAmount(100, 4) === 104); 
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Non Pure function 
const assert = require('assert');

const configs = {
  YEARLY_INTEREST_RATE: 4.0
};

const getSavingsAmount = amount => {
  return amount + amount * (configs.YEARLY_INTEREST_RATE / 100);
};

assert(getSavingsAmount(100) === 104);

configs.YEARLY_INTEREST_RATE = 3.0;

assert(getSavingsAmount(100) === 104);
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composition example 
const getSimpleText = text => {
  return text.toString().toLowerCase();
};

const getCurrentDateTime = () => new Date().toISOString();

const loggerWithTimeStamp = text => getCurrentDateTime() + ':  ' + getSimpleText(text);

const loggerWithTimeStampAndLevel = (text, level) => ` [ ${level.toUpperCase()} ] ${loggerWithTimeStamp(text)}`;

const loggerWithTimeStampAndLevelAndCallee = (text, level, callee) => {
  return 'Task: ' + callee + loggerWithTimeStampAndLevel(text, level);
};

const log = function(text, level) {
  if (level) {
    console[level](
      loggerWithTimeStampAndLevelAndCallee(text, level, log.caller.name)
    );
  } else {
    console.info(
      loggerWithTimeStampAndLevelAndCallee(text, 'info', log.caller.name)
    );
  }
};

(function run() {
  log('This is logger statement');
  log(Buffer.from('Something to log'), 'warn');
  log('This is logger statement', 'error');
  log('This is logger statement', 'error');
  log('This is logger statement', 'error');
})();
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Event Loop 
while (true) {
  const task = tasks().remove();
  execute(task);
}

Similiar Collections

String Magic

 @frogblog #javascript
How to Get the Domain From A URL Using Javascript Capitalize the first letter of a String Check String contains Substring Method

Things you can do with Arrays

 @mishka #javascript
Get average value of items in a javascript array How to Access Clicked Element From an Array With the Same Class Function to find the minimum value in Javascript Arrays Function to find maximum value in javascript array Get sum of all values in javascript array mongodb - How to find items using regex in Mongoose for partial text search

Time and Dates

 @new_roman11 #javascript
How to Get Current Year in Javascript How to dynamically update your site's copyright year Display Date Objects in Shorter Format - MMM DD YYY HH:MM

JS Methods for Numbers

 @goblindoom95 #javascript
toString() - Convert numbers to string toExponential() - Round off numbers in exponential notation toFixed() Method - convert number to string with fixed number of decimal places The valueOf() Method - Returns number of mathematical expression or number variable parseInt() Method - returns a whole number from a string

Dealing with JSON

 @mishka #javascript
Creating a JSON Object in Javascript JSON.stringify() - convert objects into JSON JSON.parse() - convert string into a JavaScript object

Gurukula

 @noobj #javascript
eventloop_async_blocking.js eventloop_unblocking_event_loop.js macro_and_micro_tasks.js macro_and_micro_tasks.js racer.js process.tick over setImmediate process.tick starving others Good fellow setImmediate setTimeout issue setTimeout issue Non Pure function Pure function mutating function side affects non mutating function, no side affects Immutable examples Immutable examples Immutable examples Higher order functions Higher order functions Higher order functions Higher order functions Higher order functions Test pure functions composition example Pure function Non Pure function composition example Event Loop