javascript 访问深层嵌套的属性

Posted 2021-05-03

function get(obj, props, def) {
  if (obj == null || typeof props !== "string") return def;
  const temp = props.split(".");
  const fieldArr = [].concat(temp);
  temp.forEach((e, i) => {
    if (/^(\w+)\[(\w+)\]$/.test(e)) {
      const matches = e.match(/^(\w+)\[(\w+)\]$/);
      const fieldOne = matches[1];
      const fieldTwo = matches[2];
      const index = fieldArr.indexOf(e);
      fieldArr.splice(index, 1, fieldOne, fieldTwo);
    }
  });
  return fieldArr.reduce((pre, cur) => {
    const target = pre[cur] || def;

    if (target instanceof Array) {
      return [].concat(target);
    }

    if (target instanceof Object) {
      return Object.assign({}, target);
    }

    return target;
  }, obj);
}

// test
var c = { a: { b: [1, 2, 3] } };
get(c, "a.b"); // [1,2,3]