JavaScript Methods

String Methods

Math.random()	Returns a number between 0 and 1
Math.floor()	returns the largest integer less than or equal to the given number
.toUpperCase()	returns a string in all capital letters
.trim()
.startsWith()
Number.isInteger()

Number Methods

Array Methods

Methods	Explaination	Example	Example Output
.length	returns the length (size)	[1, 2, 3]	“
.push()	adds an element at the end	[1, 2, 3]	“
.pop()	removes the last element	[1, 2, 3]	“
.shift()	removes the first element		“
.unshift()	adds the specified elements to the beginning		“
.concat()	merge two or more arrays		“
.join()	creates a new string by concatenating all of the elements in this array		“
.slice()	returns a shallow copy of a portion of an array into a new array object selected from start to end		“
.indexOf()	returns the first index at which a given element can be found in the array		“
.includes()	determines whether an array includes a certain value among its entries		“
.find()	returns the first element in the provided array that satisfies the provided testing function		“
.findIndex()	returns the index of the first element in an array that satisfies the provided testing function		“
.map()	creates a new array populated with the results of calling a provided function on every element in the calling array		“
.filter()	creates a shallow copy of a portion of a given array, filtered down to just the elements from the given array that pass the test implemented by the provided function		“
.reduce()	executes a user-supplied “reducer” callback function on each element of the array		“
.every()	tests whether all elements in the array pass the test		“
.some()	tests whether at least one element in the array passes the test implemented		“
.reverse()	reverses an array		“
.at()	takes an integer value and returns the item at that index, allowing for positive and negative integers		“

.reduce

const newNumbers = [1, 3, 5, 7]; 
 
const newSum = newNumbers.reduce((accumulator, currentValue) => {
  console.log("The value of accumulator: ", accumulator);
  console.log("The value of currentValue: ", currentValue);
  return currentValue + accumulator;
 
});
 
console.log(newSum)
 
//The value of accumulator:  1
//The value of currentValue:  3
//The value of accumulator:  4
//The value of currentValue:  5
//The value of accumulator:  9
//The value of currentValue:  7
//re16

Example

const cities = ["Orlando", "Dubai", "Edinburgh", "Chennai", "Accra", "Denver", "Eskisehir", "Medellin", "Yokohama",
];
 
const nums = [1, 50, 75, 200, 350, 525, 1000];
 
//  Choose a method that will return undefined
cities.forEach((city) => console.log("Have you visited " + city + "?"));
 
// Choose a method that will return a new array
const longCities = cities.filter((city) => city.length > 7);
 
// Choose a method that will return a single value
const word = cities.reduce((acc, currVal) => {
  return acc + currVal[0];
}, "C");
 
console.log(word);
 
// Choose a method that will return a new array
const smallerNums = nums.map((num) => num - 5);
 
// Choose a method that will return a boolean value
nums.every((num) => num < 0);