JavaScript Utility Functions

util.js

function findCssRule(selectorText)
{
  for (let styleSheet of document.styleSheets)
    for (let cssRule of styleSheet.cssRules) 
      if (cssRule.selectorText === selectorText)
        return cssRule;
  throw Error(`Rule with selectorText '${selectorText}' is not found`);
}

/**
  Chainable function `on`
  
  Usage:

  let els = document.querySelectorAll('div');
  let listener = e => console.log(e.target.textContent, e.type);

  let rels = on('click', listener, null, els)
    .on('mouseover', listener)
    .on('mouseout', listener)
    .els;

  console.log(els === rels); // true
*/  
 function on(type, listener, options, els)
 {
   let ob =
     {
       on(type, listener, options)
       {
         for (let el of els)
           el.addEventListener(type, listener, options);
         return this;
       },
       els
     };
   return ob.on(type, listener, options);
 }

function split(str, sepChar, escChar)
{
  if (sepChar.length !== 1)
    throw new Error(`sepChar[${sepChar}] length should be exactly 1`);
  if (escChar.length !== 1)
    throw new Error(`escChar[${escChar}] length should be exactly 1`);
  if (sepChar === escChar)
    throw new Error(`sepChar[${sepChar}] and escChar should not be same`);

  let part = '', parts = [];
  for (let i = 0, len = str.length, nc; i < len; i++)
  {
    let c = str[i];
    if (c === sepChar)
    {
      parts.push(part);
      part = '';
      continue;
    }

    if (c === escChar)
    {
      if ((i + 1) < len && ((nc = str[i + 1]) === sepChar || nc === escChar))
      {
        part += nc;
        i++;
        continue;
      }

      // Strict implementation should throw exception here as escChar is not escaped properly
    }

    part += c;
  }
  parts.push(part);

  return parts;
}

/**
Usage:

  for (let childElPathsAry of childElPaths([document.body]))
  {
    console.log(childElPathsAry);
    for (let childElPath of childElPathsAry)
      console.log(childElPath.map(el => el.nodeName).join(' > '));
  }  
*/
function childElPaths(parentEls) // returns [[[child1, child2, ...], ], ]
{
  let childElPaths = [];
  for (let parentEl of parentEls)
  {
    let childElPathsResult = childElPaths0(parentEl, [parentEl]);
    childElPaths.push(childElPathsResult);
  }
  return childElPaths;

  function childElPaths0(parentEl, parentElPathAry) // returns [[child1, child2, ...], ]
  {
    let children = parentEl.children;

    if (!children.length)
      return [parentElPathAry];

    let childElPaths = [];

    let lastIndex = parentElPathAry.length;
    let childElPathAry = [...parentElPathAry, null];

    for (let childEl of children)
    {
      childElPathAry[lastIndex] = childEl;
      let subChildElPaths = childElPaths0(childEl, childElPathAry); 
      childElPaths.push(...subChildElPaths);
    }

    return childElPaths;
  }
}