javascript 检查字典是否存在
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javascript check if dictionary
提问by aryan
I have a simple program like:
我有一个简单的程序，如：
var a = {'a': 1, 'b': 2}
console.log(a)
console.log(a instanceof Array)
console.log(a.constructor instanceof Array)
Here value of ais dictionary. I want to check for it.
这里的值a是字典。我想检查一下。
How can I check in javascript. My both test above gives me false value
我如何检查javascript。我上面的两个测试都给了我错误的值
I am new to javascript
我是 javascript 新手
回答by Floyd
回答by kofifus
function isDict(v) {
return typeof v==='object' && v!==null && !(v instanceof Array) && !(v instanceof Date);
}
回答by jfriend00
The structure {'a': 1, 'b': 2}is a Javascript object. It can be used sort of like a dictionary, but Javascript does not have an actual dictionary type.
该结构{'a': 1, 'b': 2}是一个 Javascript 对象。它可以像字典一样使用，但 Javascript 没有实际的字典类型。
console.log(typeof a); // "object"
console.log(Array.isArray(a)); // false, because it's not an array
If you want to know if something is an array, then use:
如果你想知道某个东西是否是一个数组，那么使用：
Array.isArray(a)
If you want to know if something is an object, then use:
如果您想知道某物是否是对象，请使用：
typeof a === "object"
But, you will have to be careful because an Array is an object too.
但是，您必须小心，因为 Array 也是一个对象。
If you want to know if something is a plain object, you can look at what jQuery does to detect a plain object:
如果你想知道某个东西是否是一个普通对象，你可以看看 jQuery 是如何检测一个普通对象的：
isPlainObject: function( obj ) {
// Not plain objects:
// - Any object or value whose internal [[Class]] property is not "[object Object]"
// - DOM nodes
// - window
if ( jQuery.type( obj ) !== "object" || obj.nodeType || jQuery.isWindow( obj ) ) {
return false;
}
// Support: Firefox <20
// The try/catch suppresses exceptions thrown when attempting to access
// the "constructor" property of certain host objects, ie. |window.location|
// https://bugzilla.mozilla.org/show_bug.cgi?id=814622
try {
if ( obj.constructor &&
!hasOwn.call( obj.constructor.prototype, "isPrototypeOf" ) ) {
return false;
}
} catch ( e ) {
return false;
}
// If the function hasn't returned already, we're confident that
// |obj| is a plain object, created by {} or constructed with new Object
return true;
},
回答by Sohail Si
To be more rigorous you can use JSON. But it's not a performance & memory efficient solution:
为了更严格，您可以使用 JSON。但这不是性能和内存高效的解决方案：
function isJsonable(v) {
try{
return JSON.stringify(v) === JSON.stringify(JSON.parse(JSON.stringify(v)));
} catch(e){
/*console.error("not a dict",e);*/
return false;
}
}
So the answer can be: (note that it is an inefficient method and is recommended for test purposed only)
所以答案可以是：（请注意，这是一种低效的方法，建议仅用于测试目的）
function isDict(v) {
return !!v && typeof v==='object' && v!==null && !(v instanceof Array) && !(v instanceof Date) && isJsonable(v);
}
回答by Jagannath Swarnkar
You can use this to check either your dict(data) is a dictionary or not !
您可以使用它来检查您的 dict(data) 是否是字典！
var dict = { a: 1, b: { c: 3, d: 4 }, e: 9 };
// this function will true / false
const isDict = dict => {
return typeof dict === "object" && !Array.isArray(dict);
};
console.log(isDict(dict)); // true
this will return you true if it is a dictionary otherwise return false
如果它是字典，这将返回 true 否则返回 false
回答by Pavan Varyani
I use the toStringmethod in Object.prototype, works like a charm in all the cases(Array,null,undefined etc).
我在 Object.prototype 中使用toString方法，在所有情况下（数组、空值、未定义等）都像一个魅力。
var array_var=[1,2];
var dict_var={
'a':'hey',
'b':'hello'
};
console.log(Object.prototype.toString.call(dict_var) === '[object Object]');//returns true
console.log(Object.prototype.toString.call(array_var) === '[object Object]');//returns false
In short the toString method is used to represent the object, for example the toString method for an array returns '[object Array]'
总之toString方法是用来表示对象的，比如数组的toString方法返回'[object Array]'
回答by David Alvarez
Would that work ?
那行得通吗？
function isDictObj(obj: any) {
try {
const test = {...obj}
} catch(err) {
return false
}
return true
}
My logic is that if it is a dictionnary object (key:values), then using spread operator with {} should work, otherwise throw an exception
我的逻辑是，如果它是一个字典对象 (key:values)，那么使用带有 {} 的扩展运算符应该可以工作，否则抛出异常
