Changing second half of string number digits to zero using JavaScript

Problem

We are required to write a JavaScript function that takes in a string number as the only argument.

Our function should return the input number with the second half of digits changed to 0.

In cases where the number has an odd number of digits, the middle digit onwards should be changed to 0.

For example:

938473 ? 938000

How It Works

The algorithm works by calculating the midpoint of the string. For even-length strings, exactly half the digits are preserved. For odd-length strings, the middle digit becomes part of the second half that gets zeroed out.

Example

Following is the code:

const num = '938473';
const convertHalf = (num = '') => {
    let i = num.toString();
    let j = Math.floor(i.length / 2);
    if (j * 2 === i.length) {
        return parseInt(i.slice(0, j) + '0'.repeat(j));
    } else {
        return parseInt(i.slice(0, j) + '0'.repeat(j + 1));
    };
};
console.log(convertHalf(num));

938000

Testing Multiple Cases

Let's test the function with different string lengths:

const convertHalf = (num = '') => {
    let i = num.toString();
    let j = Math.floor(i.length / 2);
    if (j * 2 === i.length) {
        return parseInt(i.slice(0, j) + '0'.repeat(j));
    } else {
        return parseInt(i.slice(0, j) + '0'.repeat(j + 1));
    };
};

console.log(convertHalf('1234'));    // Even length (4 digits)
console.log(convertHalf('12345'));   // Odd length (5 digits)  
console.log(convertHalf('678901'));  // Even length (6 digits)
console.log(convertHalf('9'));       // Single digit

1200
12000
678000
0

Simplified Version

Here's a more concise implementation:

const convertHalfSimple = (num = '') => {
    const str = num.toString();
    const halfPoint = Math.floor(str.length / 2);
    return parseInt(str.slice(0, halfPoint) + '0'.repeat(str.length - halfPoint));
};

console.log(convertHalfSimple('938473'));
console.log(convertHalfSimple('12345'));

938000
12000

Key Points

• Math.floor(length / 2) determines where to split the string
• For even lengths: first half preserved, second half zeroed
• For odd lengths: middle digit becomes part of the zeroed section
• slice(0, halfPoint) extracts the first half to keep
• '0'.repeat(count) generates the required zeros

Conclusion

This function effectively converts the second half of any numeric string to zeros using string slicing and the repeat method. The Math.floor operation handles both even and odd length strings correctly.