longest-length.js

/**
 * @param {string} s
 * @return {number}
 */
const lengthOfLongestSubstring = s => {
    let begin = 0
    let end = 1
    let final = ""

    const length = s.length + 1
    
    while(begin < length && end < length) {
        const sub = s.slice(begin, end)
        const sublen = sub.length
        const test = sub.slice(0, sublen - 1)
        const last = sub.slice(sublen - 1)

        if(test.indexOf(last) > -1 ) {
            begin++
        } else {
            if(sub.length > final.length) final = sub
            end++
        }
    } 
    
    return final.length
};