lodash源码解读util第一部分

function attempt(func, ...args) {
  try {
    return func.apply(undefined, args)
  } catch (e) {
    return isError(e) ? e : new Error(e)
  }
}

// Avoid throwing errors for invalid selectors.
var elements = _.attempt(function(selector) {
  return document.querySelectorAll(selector);
}, '>_>');
 
if (_.isError(elements)) {
  elements = [];
}

function cond(pairs) {
  const length = pairs == null ? 0 : pairs.length

  pairs = !length ? [] : map(pairs, (pair) => {
    if (typeof pair[1] != 'function') {
      throw new TypeError('Expected a function')
    }
    return [pair[0], pair[1]]
  })

  return (...args) => {
    for (const pair of pairs) {
      if (pair[0].apply(this, args)) {
        return pair[1].apply(this, args)
      }
    }
  }
}