JavaScript: Round a number to a given specific decimal places

JavaScript Math: Exercise-14 with Solution

Round Number to Decimal Place

Write a JavaScript function to round a number to decimal place.

Test Data:
console.log(precise_round(12.375,2));
console.log(precise_round(12.37499,2));
console.log(precise_round(-10.3079499, 3));
Output :
"12.38"
"12.37"
"-10.308"

Visual Presentation:

Sample Solution:

JavaScript Code:

// Reference: https://bit.ly/3zxAhnH
// Define a function named precise_round that rounds a number to a specified precision.
function precise_round(n, r) {
    // Convert the floor of n to a string.
    let int = Math.floor(n).toString();
    // Check if n or r are not numbers, if so, return 'Not a Number'.
    if (typeof n !== 'number' || typeof r !== 'number') return 'Not a Number';
    // Remove leading '+' or '-' from the integer part of n.
    if (int[0] == '-' || int[0] == '+') int = int.slice(int[1], int.length);
    // Round n to the specified precision using toPrecision method.
    return n.toPrecision(int.length + r);
}

// Output the result of rounding 12.375 to 2 decimal places to the console.
console.log(precise_round(12.375, 2));
// Output the result of rounding -10.3079499 to 3 decimal places to the console.
console.log(precise_round(-10.3079499, 3));
// Output the result of rounding 10.49999 to 0 decimal places to the console.
console.log(precise_round(10.49999, 0));
// Output the result of rounding 10.49999 to 2 decimal places to the console.
console.log(precise_round(10.49999, 2));

Output:

12.38
-10.308
10
10.50

Flowchart:

Live Demo :

See the Pen javascript-math-exercise-14 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that rounds a number to a specified number of decimal places using arithmetic operations.
• Write a JavaScript function that rounds a number and returns the result as a number, not a string.
• Write a JavaScript function that implements banker's rounding (round half to even) to a given decimal place.
• Write a JavaScript function that handles rounding for both positive and negative numbers to a fixed number of decimals.

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