使用数组的过滤功能

var Obj = [
  {"start": 0, "length": 3, "style": "text"},
  {"start": 4, "length": 2, "style": "operator"},
  {"start": 4, "length": 3, "style": "error"}
];

var result = Obj.filter(x => x.start === 4);
console.log(result);

_findItemByValue(Obj, "start", 4);

var _findItemByValue = function(obj, prop, value) {
  return obj.filter(function(item) {
    return (item[prop] === value);
  });
}

兼容除 IE6、IE7、IE8 之外的所有版本，但存在polyfill。

if (!Array.prototype.filter) {
  Array.prototype.filter = function (fn, context) {
    var i,
        value,
        result = [],
        length;

        if (!this || typeof fn !== 'function' || (fn instanceof RegExp)) {
          throw new TypeError();
        }

        length = this.length;

        for (i = 0; i < length; i++) {
          if (this.hasOwnProperty(i)) {
            value = this[i];
            if (fn.call(context, value, i, this)) {
              result.push(value);
            }
          }
        }
    return result;
  };
}