Super Useful Tips & Tricks for JavaScript Developers
Tags: javascript, react, codenewbie, node
Published: 2021-05-23 06:14:39

### Quick way to mask numbers using slice and ES8 padStart method

```js
const creditCard = "4111111111114321"; // 16 digit credit card number
const lastFourDigits = creditCard.slice(-4); // get last 4 digits

// prepend * to lastFourDigits to make length equal to creditCard number length
const maskedNumber = lastFourDigits.padStart(creditCard.length, '*');

console.log(lastFourDigits); // 4321
console.log(maskedNumber); // ************4321
```

---

## Execute an event handler only once

By passing `{ once: true }` as the third argument to the `addEventListener` method, the event handler function will be executed only once.

```js
document.getElementById("btn").addEventListener("click",
  function () {
    console.log("Button clicked!");
  },
  { once: true }
);
```

---

### Update properties of an object using spread operator 

```js
const user = {
  name: 'David',
  age: 30,
  city: 'NY'
};

const newAge = 40;

const updatedUser = {
  ...user,
  age: newAge
};

console.log(user); // { name: 'David', age: 30, city: 'NY'}
console.log(updatedUser); // { name: 'David', age: 40, city: 'NY'}
```

---

### Find the number of properties in an object

```js
const user = {
  name: 'David',
  age: 30, 
  city: 'NY'
};

console.log(Object.keys(user).length); // 3
```

----

## Get the last elements from the array

```js
const numbers = [10, 20, 30, 40, 50];
const last = numbers.slice(-1);
console.log(last); // [50]

const secondLast = numbers.slice(-2);
console.log(secondLast); // [40, 50]
```

> Note that, slice method is available for the array as well as string.

---

### Three ways to check If the provided array is actually an array

In JavaScript, array is also an object so to check If it's actually an array or object you can use the following 3 ways. (Popular Interview Question)

```js
const arr = [1, 2, 3, 4];
```

1. arr.constructor.toString().indexOf("Array") > -1
2. arr instanceof Array
3. Array.isArray(arr)

----

## Get current timestamp

```js
const date = new Date();
console.log(date.getTime()); // 1621708197268
```

The timestamp value is sometimes useful for generating unique values because the timestamp value is always different for every second.

----

### Provide a dynamic key for an object using ES6 computed object property syntax

```js
// old way
function getPairs(key, value) {
  var object = {};
  
  object[key] = value

  return object;
}

console.log(getPairs('name', 'Mike')); // { name: 'Mike'}
console.log(getPairs('age', '40')); // { age: 40}

// new ES6 way
function getPairs(key, value) {
  const object = {
    [key]: value
  };

  return object;
}

console.log(getPairs('name', 'Mike')); // { name: 'Mike'}
console.log(getPairs('age', '40')); // { age: 40}
```

---

### Object destructuring

```js
const user = {
 name: 'David',
 age: 30
};

// destructure user properties and use a `status` property with value `Married` If it does not exist
const {name, age, status = 'Married' } = user;
console.log(name, age, status) // David 30 Married

const person = {
 age: 30
};

// destructure `person` object and rename `name` to `username` and assign a default value of `Anonymous`, If the property does not exist in the `person` object
const {name: username = 'Anonymous', age } = person;

console.log(username, age); // Anonymous 30
```

----

## Array destructuring

```js
const days = ["sunday", "monday", "tuesday", "wednesday", "thursday", "friday", "saturday"];

const [firstDay, secondDay] = days;

console.log(firstDay); // sunday
console.log(secondDay); // monday
```

---

## Using ES6 template literal syntax

```js
const user = {
 name: 'David',
 age: 30,
 address: 'NY'
};

// old way: Hi, I'm David with age 30 and living in NY
console.log("Hi, I'm " + user.name + " with age " + user.age + " and living in " + user.address);

// new way: Hi, I'm David with age 30 and living in NY

console.log(`Hi, I'm ${user.name} with age ${user.age} and living in ${user.address}`);
```

This can be further simplified as shown below:

```js
const user = {
 name: 'David',
 age: 30,
 address: 'NY'
};

const { name, age, address } = user;
console.log(`Hi, I'm ${name} with age ${age} and living in ${address}`);
```

---

### Pass variable number arguments to a function

ES6 rest operator (...) converts comma-separated values into an array so the `numbers` parameter of the `add` function becomes an array. 

```js
function add(...numbers) {
 return numbers.reduce((acc, value) => {
   return acc + value;
 }, 0);
}

const sum = add(1, 2, 3, 4, 5); 
console.log(sum); // 15
```

----


### Using spread operator to create a new array

```js
const first = ["two", "three", "four"];
const second = [ "six", "seven", "eight"];

const combined = ["one", ...first, "five", ...second]
console.log(combined); // ["one", "two", "three", "four", "five", "six", "seven", "eight"]
```

----

### Fill the array with a specific value

```js
const array = Array(5).fill(false); // [false, false, false, false, false]
const array = [...Array(5).keys()] // [0, 1, 2, 3, 4, 5]
```

---


## Remove duplicates from the array

* Using Set

```js
const array = [1, 2, 2, 3, 1, 5];

const unique = [...new Set(array)];

console.log(unique); // [1, 2, 3, 5];
```

* Using array filter method

```js
const array = [1, 2, 2, 3, 1, 5];

const unique = array.filter((value, index) => {
    return array.indexOf(value) === index;
});

console.log(unique); // [1, 2, 3, 5]
```

---

## Generate random number within a particular range

* random number from 0 to 100:

```js
Math.floor(Math.random() * 100)
```

* random number from 1 to 100

```js
Math.floor(Math.random() * 100) + 1
```

* random number between min (included) and max (excluded)

```js
function getRandom(min, max) { 
  return Math.floor(Math.random() * (max - min) ) + min;
}

console.log(getRandom(10, 35)); // any random number >= 10 and < 35
```

* random number between min and max (both included)

```js
function getRandom(min, max) { 
  return Math.floor(Math.random() * (max - min + 1) ) + min;
}

console.log(getRandom(10, 35)); // any random number >= 10 and <= 35
```

----

## Print JSON in a formatted way

```js
const book = {"date": "2019–03–22","book": "Harry potter","author": "J.K.Rowling"};
console.log(JSON.stringify(book, null, 2)) // formatted with 2 spaces
```

![formatted.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1621734006279/bwrzy3FYK.png)

```js
const book = {"date": "2019–03–22","book": "Harry potter","author": "J.K.Rowling"};
console.log(JSON.stringify(book, null, '\t')) // formatted with tabs
```
![formatted_tab.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1621734074444/JD9c3ovAC.png)

----

## Implement smooth scroll to the top of the page

```js
window.scrollTo({ top: 0, left: 0, behavior: "smooth" });
```

---

## Convert any value to boolean

```js
let number1;
console.log(!!number1); // false

const number2 = 10;
console.log(!!number2); // true

const name1 = 'Tim';
console.log(!!name1); // true

const name2 = '';
console.log(!!name2); // false

const nullValue = null;
console.log(!!nullValue); // false
```

This is especially useful If you want to avoid sending `null` or `undefined` as a value to the backend.

----

## Quickly convert string to number

```js
const number = "20";
const converted = +number;

console.log(converted); // 20
```

----

## Convert string to array

```js
const name = "Mike johnson";
console.log(name.split("")); // ["M", "i", "k", "e", " ", "j", "o", "h", "n", "s", "o", "n"]

const chars = "a,b,c,d,e,f";
console.log(chars.split(",")); // ["a", "b", "c", "d", "e", "f"]
```

----

## Format number to two decimal places

```js
const number = 100.32222;
console.log(number.toFixed(2)); // 100.32
```

----

## Check if the array contains a specific value

```js
const numbers = [1, 2 ,3, 10, 50];

// old way
console.log(numbers.indexOf(3) > -1); // true as it check if 3 is present in the array

// new way
console.log(numbers.includes(3)); // true
```

The `includes` method is also useful when comparing multiple values at once.

```js
const day = "monday";
if(day === "monday" || day === "tuesday" || day === "wednesday" || day === "thursday") {
  // do something
}

// The above code is the same as the below code

const day = "monday";
if(["monday", "tuesday", "wednesday", "thursday"].includes(day)) {
  // do something
}
```

----

## Using optional chaining operator

```js
const user = {
  name: 'David',
  location: {
    street: {
      number: 20,
      name: '11 wall street'
    }
  }
};

// old way
const streetName = user.location && user.location.street && user.location.street.name;
console.log(streetName); // 11 wall street

// new way
const streetName = user?.location?.street?.name;
console.log(streetName); // 11 wall street
```
Previously, to access the nested property we need to check for each property If it exists or not because directly accessing `user.location.street.name` will throw an error If the `location` or `street` property does not exist and we try to access `name` on it like this:

```js
const user = {
  name: 'David'  
};

const streetName = user.location.street.name; // Uncaught TypeError: Cannot read property 'street' of undefined
```

But now with the ES11 optional chaining operator, the next code after `?.` will be executed only if the previous reference is not `undefined` or `null` so we don't get any error.

```js
const user = {
  name: 'David'  
};

const streetName = user?.location?.street?.name;
console.log(streetName); // undefined
```

So using the optional chaining operator makes the code shorter and easier to understand.

### Thanks for reading!

> **Want to learn Redux in detail and build a complete food ordering app? check out my [Mastering Redux](https://master-redux.yogeshchavan.dev/) course.**

Following is the preview of the app, we'll be building in the course. It's a great project you can add to your portfolio/resume.

Note that, in this app, I have used INR as the currency for displaying the prices but you can easily change it to USD or AUD or any other currency with a single configuration change in the app.

{% youtube 2zaPDfCKAvM %}

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