TypeScript array is a collection of homogenous/(same datatype) values. In simple word, typescript array can store the value of same datatype.
There are two ways to create/declare an array
Syntax : let name_of_array:data_type =[v1,v2,v3, ….,vn]
let numArrays: number[] = [101,201,301]; // number array
Syntax : let name_of_array :Array<T> =[v1,v2,v3, ….,vn]
let numArrays:Array<number>=[101,201,301];
// Created employees array with 5 values let employees : string[]=['John','Mike','Adam','Mona','Jack'] // console the length of array console.log(employees.length); // 5
let first_item= employees[0]; // get the first item of array let last_item=employees[4]; // get the last item of array let last_item_using_length =employees[employees.length -1]; // get the last item of array using array length -1 to get the last index console.log(first_item); //John console.log(last_item); //Jack console.log(last_item_using_length); //Jack console.log(employees[5]); //undefined
// loop using function employees.forEach(function(item,index){ console.log(`${item} is at ${index} Index`); }) // look using arra employees.forEach( (item,index) =>{ console.log(`${item} is at ${index} Index`); }) // John is at 0 Index // Mike is at 1 Index // Adam is at 2 Index // Mona is at 3 Index // Jack is at 4 Index
let employees : string[]=['John','Mike','Adam','Mona','Jack'] // Add element to array employees.push('Harry') console.log(employees); //[ 'John', 'Mike', 'Adam', 'Mona', 'Jack', 'Harry' ]
// Remove element from end let employees : string[]=['John','Mike','Adam','Mona','Jack'] employees.pop() console.log(employees); //[ 'John', 'Mike', 'Adam', 'Mona', 'Jack' ]
// remove 'John' from the starting let employees : string[]=['John','Mike','Adam','Mona','Jack'] employees.shift() console.log(employees); //[ 'Mike', 'Adam', 'Mona', 'Jack' ]
let employees : string[]=['John','Mike','Adam','Mona','Jack'] // add element 'John' at 0 index employees.unshift('John') console.log(employees); //[ 'John', 'Mike', 'Adam', 'Mona', 'Jack' ]
let employees : string[]=['John','Mike','Adam','Mona','Jack'] // find index of a element let indexPosition =employees.indexOf('Mike') console.log(indexPosition); //1
Property |
Description |
---|---|
from()
|
The Array.from() method creates a new Array object from any object using length property or Array type object. |
isArray()
|
The Array.isArray() method check whether the passed argument value is an Array or not. |
of()
|
The Array.of() method creates a new Array object from a variable number of arguments |
concat()
|
The concat() method is used to merge/join two or more arrays and return the new array. |
copyWithin()
|
The copyWithin() method copies array items to another position within same array without overwriting the existing values. |
entries()
|
The entries() method returns an Array Iterator object with key& value pairs of every index in the array. |
every()
|
The every() method verify all the array elements pass a test and return true/false. If all elements pass the provided test return true else false. |
fill()
|
The fill() method fills/modifies/replace all the elements of an array with a static value. It returns the updated array. |
filter()
|
The filter() method creates an array with all items that pass a test by the provided function. |
find()<
|
The find() method returns the first item in the provided array that pass the test. |
findIndex()
|
The findIndex() method returns the index of the first item in the array that pass the test. Otherwise return -1 |
flat()
|
The flat() method creates a new array with all sub-array items concatenated into it. |
flatMap()
|
The flatMap() method maps all the elements using a mapping function, then flattens the result into a new array. |
forEach()
|
The forEach() method call a provided function once for each array item. |
includes()
|
The includes() method check whether an array includes a specified value, returning true or false |
indexOf()
|
The includes() method check whether an array includes a specified value, returning true or false |
join()
|
Joins all items of an array into a string. |
keys()
|
Returns an array Iteration object with containing the keys of original array. |
lastIndexOf()
|
Search the array for an item and returns the last index of matched item. |
map()
|
Creates a new array with the results of calling a function for each array item. |
pop()
|
Removes/Delete the last item from an array. |
push()
|
Add new item in array at the end position. |
reduce()
|
Reduce the item of an array to a single value from left-to-right. |
reduceRight()
|
Reduce the item of an array to a single value from right-to-left. |
reverse()
|
Reverses the order of the items in an array. |
shift()
|
Remove/delete the first item from an array. |
slice()
|
returns the selected item in an array, as a new array. |
some()
|
Verify if any of the items in an array passes the test by provided function. |
sort()
|
Sorts the items of an array. |
splice()
|
Add/delete elements from an array and modify the original array. |
toString()
|
Converts an array to a comma separated string. |
unshift()
|
Adds new item at 0 position of array. |
values()
|
Returns new Array Iteration Object, containing the values of the original array. |
The Array.from() method creates a new Array object from any object using length property or Array type object.
let str1 ='Hello TypeScript'; let num_arr=[101,201,301] console.log(Array.from(str1)); //output : [ 'H', 'e', 'l', 'l', 'o', ' ', 'T', 'y', 'p', 'e', 'S', 'c', 'r', 'i', 'p', 't'] console.log(Array.from(num_arr)); //output : [ 101, 201, 301 ]
The Array.isArray() method check whether the passed argument value is an Array or not.
console.log(Array.isArray({id: 101,name:'John'})); //output :false console.log(Array.isArray('Hello TypeScript')); // output : false console.log( Array.isArray(undefined)); // output : false console.log(Array.isArray(true)); // output : false console.log(Array.isArray(null)); // output : false
The Array.of() method creates a new Array object from a variable number of arguments
console.log(Array.of(5)); //output : [ 5 ] console.log(Array.of(101, 201, 301)); //output : [ 101, 201, 301 ] console.log(Array(7)); //output : [ <7 empty items> ] console.log( Array(1, 2, 3)); //output : [ 1, 2, 3 ]
The concat() method is used to merge/join two or more arrays and return the new array.
let emp_arr1 : string[]=['John','Mike'] let emp_arr2 : string[]=['Adam','Mona','Jack'] let comcat_arr =emp_arr1.concat(emp_arr2) console.log(comcat_arr); //output : [ 'John', 'Mike', 'Adam', 'Mona', 'Jack' ]
The copyWithin() method copies array items to another position within same array without overwriting the existing values.
let employees : string[]=['John','Mike','Adam','Mona','Jack'] let employees1 : string[]=['John','Mike','Adam','Mona','Jack'] let result1 = employees.copyWithin(0,2,4); // Copy to 0 index start from index 2 and copy till index 4 let result2 = employees1.copyWithin(0,3); // Copy to 0 index start from index 3 to end of array console.log(result1); // output : [ 'Adam', 'Mona', 'Adam', 'Mona', 'Jack' ] console.log(result2); // output : [ 'Mona', 'Jack', 'Adam', 'Mona', 'Jack' ]
The entries() method returns object of an Array Iterator with key & value pairs of every items in the array.
let employees : string[]=['John','Mike','Adam','Mona','Jack'] let iterator1 = employees.entries(); console.log(iterator1); // output : Object [Array Iterator] {} console.log(iterator1.next().value); //output : [ 0, 'John' ] console.log(iterator1.next().value); //output : [ 1, 'Mike' ] for(let x of iterator1){ console.log(x); // console all the key and value } //output : // [ 0, 'John' ] // [ 1, 'Mike' ] // [ 2, 'Adam' ] // [ 3, 'Mona' ] // [ 4, 'Jack' ]
The every() method verify all the array elements pass a test and return true/false. If all elements pass the provided test return true else false.
let num_arr1 =[2,4,6,8,10] let num_arr2 =[2,4,6,8,11] // check all the numbers are even number and return the true value if condition satisfied let result = num_arr1.every( x=> {return x%2 ==0}); console.log(result); // output : true let result1 = num_arr2.every( x=> {return x%2 ==0}); console.log(result1); // output : false
The fill() method fills/modifies/replace all the elements of an array with a static value. It returns the updated array.
let employees : string[]=['John','Mike','Adam','Mona','Jack'] let result1 = employees.fill('Luca',3,4) // Fill the 'luca' from index 3 until 4 console.log(result1); // output :[ 'John', 'Mike', 'Adam', 'Luca', 'Jack' ] let result2 = employees.fill('Harry',3) // Fill the 'Harry' from index 3 to end of array console.log(result2); // output :[ 'John', 'Mike', 'Adam', 'Harry', 'Harry' ] let result3 = employees.fill('Lisa') // Fill the 'Lisa to all elements of array console.log(result3); // output :[ 'Lisa', 'Lisa', 'Lisa', 'Lisa', 'Lisa'
The filter() method creates an array with all items that pass a test by the provided function.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] let result = employees.filter( item => item.length >4) // Filter all the item with length greater than 4 console.log(result); // Output : [ 'Michael', 'Oliver' ]
The find() method returns the first item in the provided array that pass the test.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] let result = employees.find( item => item.length >4) // find the first item with length greater than 4 console.log(result); // Output : Michael
The findIndex() method returns the index of the first item in the array that pass the test. Otherwise return -1
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] let result = employees.findIndex( item => item.length >6) // find the index of item which length has greater than 6 console.log(result); // Output : 3
The forEach() method call a provided function once for each array item.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] employees.forEach(item =>{ console.log(item); }) // Output : // John // Mike // Adam // Michael // Oliver
The indexOf() method returns the first index of specified item which isfound in the array, otherwise -1 if it is not present in array.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] console.log(employees.indexOf('John')); // output : 0 console.log(employees.indexOf('Adam')); // output : 2 console.log(employees.indexOf('Oliver')); // output : 4 console.log(employees.indexOf('Lisa')); // output : -1
Joins all items of an array with comma separated and return the merged string
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] let result= employees.join(); // join the array using default separator(',') let result1= employees.join('|'); // join the array using passed parameter('|') console.log(result); // outout : John,Mike,Adam,Michael,Oliver console.log(result1); // output : John|Mike|Adam|Michael|Oliver
Returns an array Iteration object with containing the keys of original array.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] let allkeys = employees.keys(); console.log(allkeys); // output : Object [Array Iterator] {} for(let key of allkeys){ console.log(key); } // output // 0 // 1 // 2 // 3 // 4
Search the array for an item and returns the last index of matched item.
const animals = ['Dodo', 'Tiger', 'Penguin', 'Dodo']; console.log(animals.lastIndexOf('Dodo')); // expected output: 3 console.log(animals.lastIndexOf('Tiger')); // expected output: 1
Creates a new array with the results of calling a function for each array item.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] let result = employees.map(item=> item) console.log(result); let num_arr = [2, 4,9,101 ]; let result1 = num_arr.map(item => item * 2); console.log(result1);
Removes/Delete the last item from an array.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] console.log(employees); // output : [ 'John', 'Mike', 'Adam', 'Michael', 'Oliver' ] employees.pop() // remove the last item of array 'Oliver' console.log(employees); // output : [ 'John', 'Mike', 'Adam', 'Michael' ]
Add new item in array at the end position.
console.log(employees); // output : [ 'John', 'Mike', 'Adam', 'Michael', 'Oliver' ] employees.push('Luca') // add an item to array in last 'Luca' console.log(employees); // output : [ 'John', 'Mike', 'Adam', 'Michael', 'Oliver', 'Luca' ]
Reduce the item of an array to a single value from left-to-right.
let num_arr = [2, 4,9,101 ]; // 2+ 4+9+101 let result = num_arr.reduce( (total,currentValue)=> total + currentValue); console.log(result); // output 116 let num_arr1 = [2, 4,9,101 ]; const sumtotal = (total,currentValue) => total + currentValue; // 5+2+ 4+9+101 let result1 = num_arr1.reduce( sumtotal,5); console.log(result1); // output : 121
Reduce the item of an array to a single value from right-to-left.
let num_arr = [2, 4,9,101 ]; // 101 -9-4-2 let result = num_arr.reduceRight( (total,currentValue)=> total - currentValue); console.log(result); // output 86 let num_arr1 = [2, 4,9,101 ]; const sumtotal = (total,currentValue) => total - currentValue; // 5- 101 -9-4-2 let result1 = num_arr1.reduceRight( sumtotal,5); console.log(result1); // output : -111
Reverses the order of the items in an array.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] let result = employees.reverse(); console.log(result); //[ 'Oliver', 'Michael', 'Adam', 'Mike', 'John' ]
Remove/delete the first item from an array.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] let result = employees.shift(); console.log(result); // output : John
returns the selected item in an array, as a new array.
let employees: string[] = ['John', 'Mike', 'Adam', 'Michael', 'Oliver'] let result = employees.slice(3); console.log(result); //[ 'Michael', 'Oliver' ] let result1 = employees.slice(3, 4); console.log(result1); // [ 'Michael' ] let result2 = employees.slice(1, 4); console.log(result2); //[ 'Mike', 'Adam', 'Michael' ]
Verify if any of the items in an array passes the test by provided function.
let num_arr1 =[2,4,6,8,10] let num_arr2 =[2,4,6,8,11] let result = num_arr1.some( x=> {return x%2 ==0}); // checks whether an element is even or not console.log(result); // output : true let result1 = num_arr2.some( x=> {return x%2 ==0}); // checks whether an element is even or not console.log(result1); // output : false
Sorts the items of an array.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] let result = employees.sort(); console.log(result); // output : [ 'Adam', 'John', 'Michael', 'Mike', 'Oliver' ]
Adds/delete elements from an array and modify the original array.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] let employees1 : string[]=['John','Mike','Adam','Michael','Oliver'] employees.splice(1,0,'Lisa'); console.log(employees); // [ 'John', 'Lisa', 'Mike', 'Adam', 'Michael', 'Oliver' ] employees1.splice(2,1,'Harry'); console.log(employees1); //[ 'John', 'Mike', 'Harry', 'Michael', 'Oliver' ]
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] let result =employees.toLocaleString() console.log(result); //John,Mike,Adam,Michael,Oliver
Converts an array to a comma separated string.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] let result =employees.toString() console.log(result); //John,Mike,Adam,Michael,Oliver
Adds new item at 0 position of array.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] employees.unshift('Lisa') console.log(employees); //[ 'Lisa', 'John', 'Mike', 'Adam', 'Michael', 'Oliver' ]
Returns new Array Iteration Object, containing the values of the original array.
let employees : string[]=['John','Mike','Adam','Michael','Oliver'] let iterator =employees.values() console.log(iterator); //Object [Array Iterator] {} for(let emp of iterator){ console.log(emp); } // output // John // Mike // Adam // Michael // Oliver