TypeScript Arrays
TypeScript Arrays are collections of similar type objects. Members of an array are called elements. Elements of an array could be accessed using their index (position of the element from the first element).
For example, an array of marks of a student can contain marks scored in different subjects.
In this tutorial, we shall learn the following actions of an array :
- Declare an Array
- Initialize the Array
- Read or access elements of Array
- Update elements of the Array
- TypeScript Array Methods
Declare an Array
An array can be declared like any other variable. Datatype of the array is optional. Following is the syntax :
var array_name[:datatype]
var
is the keyword to declare a variablearray_name
is the name of the array. We can use this name to reference the array in the program.datatype
is the datatype of the array.number[]
,string[]
, etc
Some of the examples for TypeScript Array declaration are :
var arr1 var arr2:string var arr3:int
Initialize the Array
In TypeScript, an array can be initialized during its declaration or separately.
To initialize a variable during its declaration, following is the syntax :
var array_name[:array_data_type] = [element1, element2, . ., elmentN]
To initialize a variable after its declaration, following is the syntax :
var array_name[:array_data_type] array_name = [element1, element2, . ., elmentN]
Examples are :
var marks1 = [58, 68, 74, 88, 64, 90] var marks2:number[] = [58, 68, 74, 88, 64, 90] var marks3:number[] marks3 = [58, 68, 74, 88, 64, 90] var students:string[] = ["Roshan", "Aditya", "Anisha", "Midhuna"]
Read or access elements of Array
Use index of elements to access elements of TypeScript Array.
example.ts
var marks:number[] = [58, 68, 74, 88, 64, 90] console.log(marks[0]) console.log(marks[1]) console.log(marks[2]) console.log(marks[3])
Output
58 68 74 88
Size of the array is 6. Index range is [0, 5].
Update elements of the Array
To update elements of TypeScript array, use assignment operator.
example.ts
var marks:number[] = [58, 68, 74, 88, 64, 90] marks[0] = 65 marks[1] = 68 marks[2] = 73 marks[3] = 74 console.log(marks[0]) console.log(marks[1]) console.log(marks[2]) console.log(marks[3])
Output
65 68 73 74
Methods of TypeScript Array
TypeScript provides many methods to manipulate Arrays. We shall go through each of them with examples.
concat() – Concatenates elements or arrays to the array
Array.concat() concatenates the array passed as argument to the array.
example.ts
var marks1:number[] = [58, 68, 74, 88, 64, 90] var marks2:number[] = [82, 67] var marks:number[] = marks1.concat(marks2) console.log(marks)
Output
marks : 58, 68, 74, 88, 64, 90, 82, 67
every() – Applies a function on every element of array and returns a boolean
Array.every() applies a function to every element of the array. every() returns true if all the function calls on elements return true. If function call on any of the element returns false, every() returns false.
example.ts
var marks:number[] = [58, 68, 74, 88, 64, 90] function isPassed(element, index, array) { return (element >= 35) } var passed = marks.every(isPassed) if(passed) console.log("The student has passed.") else console.log("The student has failed")
Output
The student has passed.
forEach() – Applies a function on every element of array
Array.forEach() applies a function to every element of the array. forEach() is used to apply a transformation on an array.
example.ts
var marks:number[] = [58, 68, 26, 88, 27, 90] function isPassed(value) { if(value >= 35) return true else return false } var passA = marks.forEach(isPassed) console.log(passA)
Output
passA : true, true, false, true, false, true
Conclusion
In this TypeScript Tutorial – TypeScript Arrays, we have learnt how to declare and initialize Arrays, access elements of the array, modify them, and also different methods TypeScript provides for Arrays.