Week 4

Week-3/exercise-1.js

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+/* creating the memoise function */
+
+function memoise(fn) {
+    const cache = new Map();
+
+    return function(...args) {
+        const key = args.toString();
+
+        cache.has(key) ? cache.get(key) : cache.set(key, fn(args));
+        return cache.get(key);
+    };
+}
+
+
+function add(a,b){
+    return a+b;
+}
+
+const memoiseAdd = memoise(add);
+
+console.time();
+memoiseAdd(100,100);
+console.timeEnd();
+
+memoiseAdd(100);
+memoiseAdd(100, 200);
+
+console.time();
+memoiseAdd(100,100);
+console.timeEnd();

Week-3/exercise-2.js

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+// Using Bind.
+function sum(a, b) {
+    return this.a + this.b;
+}
+
+const sumB = sum.bind({ a:10, b:25});
+
+console.log(sumB()); // ==>35
+
+/****************************************/
+
+// Using Call
+function elevate() { 
+    var offer = [   //this == object
+        this.name, 
+        'have been elevated to Manager position'
+    ].join(' ');
+
+    console.log(offer);
+}
+
+var Arun = {
+    name: 'arun'
+};
+
+var Dhanush = {
+    name: 'dhanush'
+};
+
+elevate.call(Arun);
+elevate.call(Dhanush);
+
+/*******************************************/
+
+// Using apply.
+let numbers = [88, 64, 212, 416, 432];
+
+let max = Math.max.apply(null, numbers);
+console.log(max);

Week-3/exercise-3.js

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+function createIncrement() {
+    let count = 0;
+
+    function increment() {
+        count++;
+    }
+
+    let message = `count is ${count}`;
+
+    function log() {
+        console.log(message);
+    }
+
+    return [increment, log];
+}
+
+//calling the function.
+const [increment, log] = createIncrement();
+/* 1.variable count is created and initialized with a value: 0,
+    2. function increment() is created but not called,
+    3. String message is created (at this stage, since function increment() is  not yet called, the body part of that increment() function is not executed) as message = "count is 0";,
+    4. function log() is created but not called,
+    5. returns both increment() and log() functions.
+*/
+
+increment(); // value of the count is incremented to count: 1.
+increment(); // value of the count is incremented to count: 2.
+increment(); // value of the count is incremented to count: 3.
+log();
+/*
+according to the instructions written in the body part of the log()
+function, it should display the value of the message in the console and if you see the line-21, the value of the message is "count is 0" and is displayed as 'count is 0'.
+*/
+
+
+// Answer:  count is 0

Week-4/exercise-1.js

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+/*
+Exercise-4.1:
+    Implement a function named 'getNumber' which generatesa random number. If randomNumberis divisible by 5 it will reject the promise else it will resolve the promise. Let’s also keep thepromise resolution/rejection time as a variable.
+
+    1.JS promises should not be used.
+    2.A custom promise function should be created.
+    3.This function should be able to handle all 3 states Resolve, Reject and Fulfilled.
+    4.Should be able to accept callbacks as props.
+*/
+
+function getRandomNumber() {
+  return Math.floor(Math.random() * 11);
+}
+
+//creating the state object.
+const STATE = {
+  PENDING: "PENDING",
+  RESOLVED: "RESOLVED",
+  REJECTED: "REJECTED",
+};
+
+class Pramise {
+  //callback is a function.
+  state = STATE.PENDING; //Initial state of Promise is empty.
+  value = undefined;
+  then_callbacks = [];
+  catch_callbacks = [];
+
+  constructor(callback) {
+    //Invoking the callback function by passing the presolve and the preject function of our class.
+    try {
+      callback(this.risolve, this.riject);
+    } catch (error) {
+      this.riject(error);
+    }
+  }
+
+  //risolve() method.
+  risolve(value) {
+    this.updateState(value, STATE.RESOLVED);
+  }
+
+  //riject() method.
+  riject(error) {
+    //error is usually an Object (eg: new Error('message');)
+    this.updateState(error, STATE.REJECTED);
+  }
+
+  /* creating the updateState() method */
+  updateState(value, state) {
+    if (this.state !== STATE.PENDING) return;
+
+    this.value = value;
+    this.state = state;
+  }
+
+  execute_callbacks() {
+    if (this.state === STATE.RESOLVED) {
+      this.then_callbacks.forEach((callback) => {
+        callback(this.value);
+      });
+      this.then_callbacks = [];
+    } else {
+      this.then_callbacks.forEach((callback) => {
+        callback(this.value);
+      });
+      this.then_callbacks = [];
+    }
+  }
+
+  then(then_cb, catch_cb) {
+    if (this.then_cb !== null) this.then_callbacks.push(callback);
+    else this.catch_callbacks.push(callback);
+    this.execute_callbacks();
+    return new Pramise(callback);
+  }
+
+  catch(onFail) {}
+}

Week-4/exercise-2.js

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+class Person {
+    constructor (name) {
+        this.name = name;
+    }
+
+    getName() {
+        return this.name;
+    }
+
+    setName(name) {
+        if(typeof name !== 'string') {
+            throw new Error(`Dhyaaaaan De!`);
+        } else this.name = name;
+    }
+}
+
+class Teacher extends Person {
+    teach(subject) {
+        console.log(`${this.name} is now teaching ${subject}`);
+    }
+}
+
+const ajeesh = new Teacher('Ajeesh');
+ajeesh.teach('Mathematics!');

Week-4/exercise-3.js

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+const Fibonacci = {
+  number: 5,
+  [Symbol.iterator]: function () {
+    let i = 1,
+      older = 0,
+      newer = 0;
+    return {
+      next: () => {
+        if (i++ <= this.number) {
+          [older, newer] = [newer, older + newer || 1];
+          return { value: older, done: false };
+        } else return { done: true };
+      },
+    };
+  },
+};
+
+for (let num of Fibonacci) {
+  console.log(num);
+}