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[JS] Js types 辨別型別的方法

  • typeof​

    缺點：無法辨別 object, array, null, 因為都會回傳 object.

        typeof string:string
        typeof bool: boolean
        typeof num: number
        typeof undefined: undefined
        typeof function: function
        typeof array: object
        typeof obj: object
        typeof null: object(a bug in Js)
        typeof Symbol('symbol'): symbol

解決方法​

  • 利用 typeof 特性​

typeof yourVariable === "object" &&
  !Array.isArray(yourVariable) &&
  yourVariable !== null;

  • Object.prototype.toString.call()​

    原理：Js 各個 types 都有 to string method，用 object's to string 會回傳其 type 的特型來辨別型別。
const dataTypeChecker = (data) => {
  let result = ``;
  const typeString = Object.prototype.toString.call(data);
  result = typeString.replace(/\[object /gi, ``).replace(/\]/gi, ``);
  return result;
};

[JS] Js types 辨別空 array, object

Array;

if (Array.length > 0) {
  //not empty
}

Object;

if (Object.keys(object).length > 0) {
  //not empty
}

https://medium.com/itsems-frontend/javascript-typeof-and-instanceof-2c68da994f6a https://stackoverflow.com/questions/8511281/check-if-a-value-is-an-object-in-javascript