Constructing a string of alternating 1s and 0s of desired length using JavaScript

Problem

We are required to write a JavaScript function that takes in a number n. Starting with '1' our function should construct a string of length n that contains '1' and '0' alternatingly.

Example

Following is the code ?

const num = 12;
const buildString = (num = 1) => {
    let res = '';
    for(let i = 0; i < num; i++){
        if(i % 2 === 0){
            res += 1;
        }else{
            res += 0;
        };
    };
    return res;
};
console.log(buildString(num));

101010101010

Alternative Methods

Using String Repetition and Slice

For better performance with larger strings, we can create the pattern once and repeat it:

const buildStringFast = (num) => {
    const pattern = '10';
    return pattern.repeat(Math.ceil(num / 2)).slice(0, num);
};

console.log(buildStringFast(8));   // Length 8
console.log(buildStringFast(15));  // Length 15

10101010
101010101010101

Using Ternary Operator

A more concise version using the ternary operator:

const buildStringTernary = (num) => {
    let result = '';
    for(let i = 0; i < num; i++){
        result += i % 2 === 0 ? '1' : '0';
    }
    return result;
};

console.log(buildStringTernary(10));
console.log(buildStringTernary(7));

1010101010
1010101

Performance Comparison

Edge Cases

// Handle edge cases
console.log(buildString(0));  // Empty string
console.log(buildString(1));  // Single character
console.log(buildString(2));  // Two characters

1
10

Conclusion

All three methods effectively create alternating strings of 1s and 0s. The string repeat method offers better performance for large strings, while the loop approach is more straightforward and easier to understand.