A simple and naive implementation of diff

naiveDiff.js

function naiveDiff(aIn, bIn, options) {
    const rawA = aIn + '' === aIn ? aIn.split('') : aIn;
    const rawB = bIn + '' === bIn ? bIn.split('') : bIn;
  	let a = rawA;
  	let b = rawB;
  	if (options.trim) {
      a = a.map(s => s.trim());
      b = b.map(s => s.trim());
    }
  	if (options.skipEmpty) {
      a = a.filter(s => s !== '');
      b = b.filter(s => s !== '');
    }
    const m = a.length;
    const n = b.length;
    let start = 0;
    while (start <= m && start <= n && a[start] == b[start]) {
      start++;
    }
    let m_end = m - start;
    let n_end = n - start;
    while (start <= m_end && start <= n_end && a[m_end] == b[n_end]) {
        m_end--;
        n_end--;
    }
    const c = Array(m_end+1).fill(0).map(x => Array(n_end+1).fill(0));
    for (let i = 1; i <= m_end; i++) {
        for (let j = 1; j <= n_end; j++) {
            if (a[i-1+start] == b[j-1+start]) {
                c[i][j] = c[i-1][j-1] + 1;
            } else {
                c[i][j] = Math.max(c[i][j-1], c[i-1][j]);
            }
        }
    }
    const out = [];
    for (let i = m_end, j = n_end; (i >= 0 && j > 0) || (i > 0 && j >= 0); ) {
        if (i > 0 && j > 0 && a[i-1+start] == b[j-1+start]) {
            out.push({action: 0, value: a[i-1+start]});
            i--;
            j--;
        } else if (j > 0 && (i === 0 || c[i][j-1] >= c[i-1][j])) {
            out.push({action: 1, value: b[j-1+start]});
            j--;
        } else if (i > 0 && (j === 0 || c[i][j-1] < c[i-1][j])) {
            out.push({action: -1, value: a[i-1+start]});
            i--;
        }
    }
    return rawA.slice(0, start)
        .map(value => ({action: 0, value}))
        .concat(out.reverse())
        .concat(rawA.slice(start+m_end).map(value => ({action: 0, value})));
}