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How to use the Array.join() method in JavaScript

Programming Bytes

The array.join() method will return a new string by concatenating all the elements of the array.

let array = ["I", "Love", "Tamil", "language"];
let joinedSting = array.join(","); // join with comma as delimiter
console.log("After joining array =", joinedSting);

The array method takes a separator as an argument. The separator will be placed between the elements of the array.

let array = ["I", "Love", "Tamil", "language"];

console.log("\n-------------\nJoining array with separator ','");
let str = array.join(',');
console.log(str);

console.log("\n-------------\nJoining array with empty space as separator");
str = array.join(''); 
console.log(str);

console.log("\n-------------\nJoining array with separator ' + ' ");
str = array.join(' + '); 
console.log(str);

console.log("\n-------------\nJoining array with space as separator ");
str = array.join(' '); 
console.log(str);

If the array only contains one element, the separator will not be added.

console.log("\n-------------\nIf there is only one element in the array, the seperator will not be added");
let array = ["Tamil"];
let str = array.join(','); 
console.log(str);

, is considered as the default separator.

console.log("\nJoining array with empty string as separator ");
let array = ["I", "Love", "Tamil", "language"];
let str = array.join(); 
console.log(str);

If the length of the array is 0, then the empty string is returned.

console.log("\n-------------\nIf the array length is 0 then empty string is returned");
let array = [];
let str = array.join('~~~~~~'); 
console.log("value after join empty array",str);

If an element of the array is undefined, null, or an empty array [], it is converted to an empty string.

console.log("If an array element is undefined or null then empty string is returned \n")
let array = [1,undefined,2,null,3,4];
let str =  array.join(",");
console.log("After joining array", array, "\nThe returned value is ", str );

All elements are converted to a string before they are joined. If the array contains an object, it is converted to a string as well.

console.log("Joining object ");
let array = [{}, [1], "1"];
let str = array.join("-");
console.log("On joining", array, "\nThe returned sting is", str);

Complete code

let array = ["I", "Love", "Tamil", "language"];

console.log("\n-------------\nJoining array with separator ','");
let str = array.join(',');
console.log(str);

console.log("\n-------------\nJoining array without separator - by default ',' is considered as separator");
str = array.join(); 
console.log(str);

console.log("\n-------------\nJoining array with separator ' + ' ");
str = array.join(' + '); 
console.log(str);

console.log("\nJoining array with empty string as separator ");
str = array.join(''); 
console.log(str);

console.log("\n-------------\nJoining array with space as separator ");
str = array.join(' '); 
console.log(str);

console.log("\n-------------\nIf there is only one element in the array seperator will not be added");
array = ["Tamil"];
str = array.join(','); 
console.log(str);

console.log("\n-------------\nIf the array length is 0 then empty string is returned");
array = [];
str = array.join('~~~~~~'); 
console.log(str);

console.log("\n-------------\nIf an array element is undefined or null then empty string is returned \n")
array = [1,undefined,2,null,3,4];
str =  array.join(",");
console.log("After joining array", array, "\nThe returned value is ", str );

console.log("\n-------------\nJoining object ");
array = [{}, [1], "1"];
str = array.join("-");
console.log("On joining", array, "\nThe returned sting is", str);

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