如何从 javascript 中的 Map object 获取特定密钥

Question

I have a map object and I would like to get the value of a specific key ( the value of key it self ) from the Map object let say we want to get 'correct'

we can get the values of 'correct' key by: question.get('correct') // return 3 but i want: someCode //return 'correct'

const question = new Map();

question.set('question','What is the latest version of javasript ?')
question.set(1,'es4')
question.set(2,'es5')
question.set(3,'es6')
question.set('correct',3)
question.set(true , 'correct Answer');
question.set(false , 'wrong Answer')

Answer 1

If your use case is just to test the existence of key then simply use has , but if you want to get key back if it present else some other value then you can use has to test key is present or not, here getKey function check if key is present on Map return that key else return Not found

 const question = new Map(); question.set('question','What is the latest version of javasript?') question.set(1,'es4') question.set(2,'es5') question.set(3,'es6') question.set('correct',3) question.set(true, 'correct Answer'); question.set(false, 'wrong Answer') let getKey = key => question.has(key)? key: 'Not found' console.log(getKey('correct')) console.log(getKey('randome key'))

You can even use [...Map.keys()] to get array of keys and then iterator over and find if the value is found or not

Answer 2

To get a key based on a value, you can iterate over map entries using Map.entries() and return the key if found.

 const question = new Map(); question.set('question','What is the latest version of javasript?'); question.set(1,'es4'); question.set(2,'es5'); question.set(3,'es6'); question.set('correct',3); question.set(true, 'correct Answer'); question.set(false, 'wrong Answer'); function getKey(map, input) { for (let [key, value] of map.entries()) { if (value === input) { return key; } } return "Not found"; } console.log(getKey(question, 3)); console.log(getKey(question, 2));

Answer 3

You can get the values of keys as follows which will get all the keys of the map object:

question.keys();