TypeScript for Loop

In TypeScript, we can iterate through iterable objects (including array, map, set, string, arguments object and so on) using various for loops.

TypeScript supports 3 kind of for loops:

  • for loop (traditional for-loop)
  • for..of loop
  • for..in loop

1. TypeScript for-loop Examples

1.1. Traditional for loop

for (first expression; second expression; third expression) {
    // statements inside loop will be executed for each iteration
}

Traditional for loop is used to execute a block of code until a specified condition (second expression) is true. After each iteration, a statement (third expression) is executed which can be used to increment or decrement the counter used in the second expression.

for (let counter = 0; counter < 5; counter++) {
  console.log ("Value of counter: " + i);
}

1.2. for..of loop

for (let val of iterable) {
  //Statements
}

This loop helps in iterating over iterable objects such as list, set, map or string. With the help of this loop, we do not need to manage a counter variable explicitly.

let myArray = [10, 20, 30]; 
 
for (let value of myArray) { 
  console.log(value); 	//10 20 30
} 
let str = "Hello World";

for (var ch of str) {
  console.log(ch);   //H e l l o  W o r l d
} 

1.3. for..in loop

for (let val in collection) {
  //Statements
}

This loop helps in iterating the indexed collections such as an array, list, or tuple. While iterating over the values, it returns an index on each iteration.

let myArray = [10, 20, 30]; 
 
for (let index in myArray) { 
  console.log(index);    //Prints indexes
  console.log(arr[index]);   //Prints values
} 

2. More Examples

2.1. Iterating through an Array

Example of using for loop to iterate over array elements.

let myArray = [10, 20, 30]; 
 
for (let value of myArray) { 
  console.log(value); 	//10 20 30
} 

2.2. Iterating through a Map

Example of using 'for...of' to iterate over map entries.

let map = new Map();
map.set("A",1);
map.set("B",2);
map.set("C",3);	

//Iterate over map keys
for (let key of map.keys()) {
    console.log(key);					//A B C
}

//Iterate over map values
for (let value of map.values()) {
    console.log(value);					//1 2 3
}

//Iterate over map entries
for (let entry of map.entries()) {
    console.log(entry[0], entry[1]);	//"A" 1 "B" 2 "C" 3
}

//Using object destructuring
for (let [key, value] of map) {
    console.log(key, value);			//"A" 1 "B" 2 "C" 3
} 

2.3. Iterating through a Set

Example of using 'for...of' to iterate over set entries.

let mySet = new Set();
mySet.add('A');
mySet.add('B');
mySet.add('C');

//Iterate over set 
for (let entry of mySet) {
    console.log(entry);		//A B C
}

2.4. Iterating through a String

Example of using 'for...of' to iterate over string. During iteration, you will get one single character from string in each loop cycle.

let blogName:string = "howtodoinjava.com";

//Iterate over set 
for (let character of blogName) {
    console.log(character);		//howtodoinjava.com
}

Drop me your questions in the comments section.

Happy Learning !!

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1 thought on “TypeScript for Loop”

  1. Hi Lokesh

    Great site. Thanks for making this. I have a suggestion. I see let being used in lot of places. Suggest you to use const instead.

    Reply

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