JavaScript Built-in functions and how they works: -

JavaScript has several "top-level" built-in functions. JavaScript also has four built-in objects: Array, Date, Math, and String. Each object has special-purpose properties and methods associated with it. JavaScript also has constructors for Boolean and Number types.
In this blog we take a look in that pool of Built-in function:

Here's a categorized list of commonly used JavaScript built-in functions based on their primary use with strings, arrays, numbers, and objects:

---

String Functions

1. charAt()

   • Purpose: Returns the character at a specified index in a string.

   • Syntax: string.charAt(index)

   • Example:

       "Hello".charAt(1); // returns 'e'
     

2. concat()

   • Purpose: Concatenates two or more strings.

   • Syntax: string1.concat(string2, string3, ...)

   • Example:

       "Hello".concat(" World"); // returns 'Hello World'
     

3. includes()

   • Purpose: Determines whether a string contains a specified value.

   • Syntax: string.includes(substring)

   • Example:

       "Hello World".includes("World"); // returns true
     

4. indexOf()

   • Purpose: Returns the index of the first occurrence of a specified value in a string.

   • Syntax: string.indexOf(substring)

   • Example:

       "Hello World".indexOf("World"); // returns 6
     

5. replace()

   • Purpose: Replaces a substring with a new substring.

   • Syntax: string.replace(oldValue, newValue)

   • Example:

       "Hello World".replace("World", "Universe"); // returns 'Hello Universe'
     

6. split()

   • Purpose: Splits a string into an array of substrings.

   • Syntax: string.split(separator)

   • Example:

       "Hello World".split(" "); // returns ['Hello', 'World']
     

7. toLowerCase()

   • Purpose: Converts a string to lowercase.

   • Syntax: string.toLowerCase()

   • Example:

       "HELLO".toLowerCase(); // returns 'hello'
     

8. toUpperCase()

   • Purpose: Converts a string to uppercase.

   • Syntax: string.toUpperCase()

   • Example:

       "hello".toUpperCase(); // returns 'HELLO'
     

9. trim()

   • Purpose: Removes whitespace from both ends of a string.

   • Syntax: string.trim()

   • Example:

       "  Hello  ".trim(); // returns 'Hello'
     

---

Array Functions

1. push()

   • Purpose: Adds one or more elements to the end of an array.

   • Syntax: array.push(element1, element2, ...)

   • Example:

       let arr = [1, 2];
       arr.push(3); // arr becomes [1, 2, 3]
     

2. pop()

   • Purpose: Removes the last element from an array and returns it.

   • Syntax: array.pop()

   • Example:

       let arr = [1, 2, 3];
       arr.pop(); // returns 3, arr becomes [1, 2]
     

3. shift()

   • Purpose: Removes the first element from an array and returns it.

   • Syntax: array.shift()

   • Example:

       let arr = [1, 2, 3];
       arr.shift(); // returns 1, arr becomes [2, 3]
     

4. unshift()

   • Purpose: Adds one or more elements to the beginning of an array.

   • Syntax: array.unshift(element1, element2, ...)

   • Example:

       let arr = [2, 3];
       arr.unshift(1); // arr becomes [1, 2, 3]
     

5. slice()

   • Purpose: Returns a shallow copy of a portion of an array.

   • Syntax: array.slice(start, end)

   • Example:

       let arr = [1, 2, 3, 4];
       arr.slice(1, 3); // returns [2, 3]
     

6. splice()

   • Purpose: Adds or removes elements from an array.

   • Syntax: array.splice(start, deleteCount, item1, item2, ...)

   • Example:

       let arr = [1, 2, 3, 4];
       arr.splice(1, 2); // removes 2 elements from index 1, arr becomes [1, 4]
     

7. forEach()

   • Purpose: Executes a function for each element in an array.

   • Syntax: array.forEach(callback)

   • Example:

       [1, 2, 3].forEach(num => console.log(num)); // logs 1, 2, 3
     

8. map()

   • Purpose: Creates a new array with the results of calling a function on every element in the array.

   • Syntax: array.map(callback)

   • Example:

       let arr = [1, 2, 3];
       let newArr = arr.map(num => num * 2); // returns [2, 4, 6]
     

9. filter()

   • Purpose: Creates a new array with all elements that pass the test implemented by the provided function.

   • Syntax: array.filter(callback)

   • Example:

       let arr = [1, 2, 3, 4];
       let even = arr.filter(num => num % 2 === 0); // returns [2, 4]
     

10. reduce()

    • Purpose: Executes a reducer function on each element of the array, resulting in a single output value.

    • Syntax: array.reduce(callback, initialValue)

    • Example:

        let arr = [1, 2, 3, 4];
        let sum = arr.reduce((acc, num) => acc + num, 0); // returns 10
      

---

Number Functions

1. parseInt()

   • Purpose: Parses a string and returns an integer.

   • Syntax: parseInt(string, radix)

   • Example:

       parseInt("10"); // returns 10
     

2. parseFloat()

   • Purpose: Parses a string and returns a floating-point number.

   • Syntax: parseFloat(string)

   • Example:

       parseFloat("10.5"); // returns 10.5
     

3. toFixed()

   • Purpose: Formats a number to a specified number of decimal places.

   • Syntax: number.toFixed(decimalPlaces)

   • Example:

       let num = 10.1234;
       num.toFixed(2); // returns '10.12'
     

4. toString()

   • Purpose: Converts a number to a string.

   • Syntax: number.toString()

   • Example:

       let num = 10;
       num.toString(); // returns '10'
     

---

Object Functions

1. Object.keys()

   • Purpose: Returns an array of a given object's own property names.

   • Syntax: Object.keys(object)

   • Example:

       let obj = { a: 1, b: 2 };
       Object.keys(obj); // returns ['a', 'b']
     

2. Object.values()

   • Purpose: Returns an array of a given object's own property values.

   • Syntax: Object.values(object)

   • Example:

       let obj = { a: 1, b: 2 };
       Object.values(obj); // returns [1, 2]
     

3. Object.entries()

   • Purpose: Returns an array of a given object's own enumerable property [key, value] pairs.

   • Syntax: Object.entries(object)

   • Example:

       let obj = { a: 1, b: 2 };
       Object.entries(obj); // returns [['a', 1], ['b', 2]]
     

4. Object.assign()

   • Purpose: Copies all enumerable own properties from one or more source objects to a target object.

   • Syntax: Object.assign(target, ...sources)

   • Example:

       let target = { a: 1 };
       let source = { b: 2 };
       Object.assign(target, source); // target becomes { a: 1, b: 2 }
     

---

In this blog we discuss very commonly used built-in functions in JavaScript . This list covers some of the most frequently used JavaScript functions categorized by their use in strings, arrays, numbers, and objects.
Thank You ,
Happy reading.