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JavaScript Methods

Examples here

Exercises here

Array Methods

  • push(): Adds one or more elements to the end of an array and returns the new length of the array.
  • pop(): Removes the last element from an array and returns that element.
  • shift(): Removes the first element from an array and returns that element.
  • unshift(): Adds one or more elements to the beginning of an array and returns the new length of the array.
  • map(): Creates a new array with the results of calling a provided function on every element in the calling array.
  • filter(): Creates a new array with all elements that pass the test implemented by the provided function.
  • reduce(): Executes a reducer function on each element of the array, resulting in a single output value.
  • forEach(): Executes a provided function once for each array element.
  • find(): Returns the value of the first element in the array that satisfies the provided testing function.
  • includes(): Determines whether an array includes a certain value among its entries, returning true or false.

More array methods can be found here.

Example of map() Method

The map() method creates a new array populated with the results of calling a provided function on every element in the calling array.

const numbers = [1, 2, 3, 4];
const doubled = numbers.map(number => number * 2);

console.log(doubled); // Output: [2, 4, 6, 8]

Example of reduce() Method

The reduce() method executes a reducer function on each element of the array, resulting in a single output value.

const numbers = [1, 2, 3, 4];
const sum = numbers.reduce((accumulator, currentValue) => accumulator + currentValue, 0);

console.log(sum); // Output: 10

String Methods

  • charAt(): Returns the character at the specified index.
  • concat(): Combines the text of two or more strings and returns a new string.
  • includes(): Determines whether one string may be found within another string, returning true or false.
  • indexOf(): Returns the index within the calling String object of the first occurrence of the specified value.
  • slice(): Extracts a section of a string and returns it as a new string.
  • split(): Divides a String into an ordered list of substrings, puts these substrings into an array, and returns the array.
  • toLowerCase(): Returns the calling string value converted to lower case.
  • toUpperCase(): Returns the calling string value converted to upper case.
  • trim(): Removes whitespace from both ends of a string.

More string methods can be found here.

Example of split() Method

The split() method divides a String into an ordered list of substrings, puts these substrings into an array, and returns the array.

const sentence = 'The quick brown fox jumps over the lazy dog.';
const words = sentence.split(' ');  // Split the sentence on each space
console.log(words[3]); // Output: fox

Number Methods

  • toFixed(): Formats a number using fixed-point notation.
  • toString(): Returns a string representing the specified Number object.
  • toExponential(): Returns a string representing the Number object in exponential notation.
  • toPrecision(): Returns a string representing the Number object to the specified precision.

More number methods can be found here.

Example of toFixed() Method

The toFixed() method formats a number using fixed-point notation.

const num = 9.656; 
const n = num.toFixed(0); // Rounds to the nearest integer
console.log(n); // Output: 10

Object Methods

  • keys(): Returns an array of a given object's own enumerable property names.
  • values(): Returns an array of a given object's own enumerable property values.
  • entries(): Returns an array of a given object's own enumerable property [key, value] pairs.
  • assign(): Copies all enumerable own properties from one or more source objects to a target object.
  • hasOwnProperty(): Returns a boolean indicating whether the object has the specified property as its own property.
  • is(): Determines whether two values are the same value, for example, to compare two objects.
  • freeze(): Freezes an object: other code cannot delete or change its properties.
  • seal(): Seals an object, preventing new properties from being added to it and marking all existing properties as non-configurable.

More object methods can be found here.

Example of keys() Method

The keys() method returns an array of a given object's own enumerable property names.

const object = { a: 1, b: 2, c: 3 };
console.log(Object.keys(object)); // Output: ['a', 'b', 'c']

Example of is() Method

The is() method determines whether two values are the same value.

console.log(Object.is('foo', 'foo')); // Output: true
console.log(Object.is({}, {})); // Output: false
console.log(Object.is(NaN, NaN)); // Output: true

JavaScript Scope

Scope determines the accessibility of variables in JavaScript. There are two types of scope:

  • Global Scope: Variables declared outside a function have global scope and can be accessed anywhere in the code.
  • Local Scope: Variables declared inside a function have local scope and can only be accessed within that function.
  • Function Scope: Variables declared inside a function have function scope and can only be accessed within that function.

Example of Global Scope

let name = 'Josue'; // Global scope

function greet() {
  console.log(`Hello, ${name}!`);
}   

greet(); // Output: Hello, Josue!

Example of Local Scope

function greet() {
  let name = 'Josue'; // Local scope
  console.log(`Hello, ${name}!`);
}
    
greet(); // Output: Hello, Josue!
console.log(name); // Output: ReferenceError: name is not defined

Example of Function Scope

function greet() {
  if (true) {
    let name = 'Josue'; // Function scope
    console.log(`Hello, ${name}!`);
  }
  console.log(name); // Output: ReferenceError: name is not defined
} 

greet();