JavaScript: Join all elements of an array into a string and returns this string

JavaScript fundamental (ES6 Syntax): Exercise-182 with Solution

Write a JavaScript program to join all elements of an array into a string and return this string. Use a separator and an end separator.

• Use Array.prototype.reduce() to combine elements into a string.
• Omit the second argument, separator, to use a default separator of ','.
• Omit the third argument, end, to use the same value as separator by default.

Sample Solution:

JavaScript Code:

// Define a function 'join' that concatenates elements of an array 'arr' into a single string
// with specified 'separator' between elements and 'end' at the end of the string
const join = (arr, separator = ',', end = separator) =>
  // Reduce the array into a single string
  arr.reduce(
    (acc, val, i) =>
      // If it's the second last element, concatenate 'end' instead of 'separator'
      i === arr.length - 2
        ? acc + val + end
        // If it's the last element, concatenate only the value without 'separator' or 'end'
        : i === arr.length - 1
          ? acc + val
          // Concatenate the value with 'separator'
          : acc + val + separator,
    '' // Start with an empty string
  );

// Print the joined string with specified separator ',' and end '&'
console.log(join(['pen', 'pineapple', 'apple', 'pen'], ',', '&'));
// Print the joined string with specified separator ','
console.log(join(['pen', 'pineapple', 'apple', 'pen'], ','));
// Print the joined string with default separator ',' and default end ','
console.log(join(['pen', 'pineapple', 'apple', 'pen']));

Output:

pen,pineapple,apple&pen
pen,pineapple,apple,pen
pen,pineapple,apple,pen

Visual Presentation:

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-182-1 by w3resource (@w3resource) on CodePen.

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