JavaScript Object.entries() ECMAScript 2017 added theObject.entries()method to objects. Object.entries()returns an array of the key/value pairs in an object: Example constperson = { firstName :"John", lastName :"Doe", age :50,
keys() Return Value The keys() method returns an array of strings that represent all the enumerable properties of the given object. Note: The ordering of the properties is the same as that when looping over them manually. Example: Using Object.keys() // Array objects const arr = ["A",...
Looping over a String Example letlanguage ="JavaScript"; lettext =""; for(letx of language) { text += x +" "; } Try it Yourself » Learn more in the chapter:JavaScript Loop For/In/Of. JavaScript Maps Being able to use an Object as a key is an important Map feature. ...
// insert key-value pair map1.set('info', {name: 'Jack', age: 26}); console.log(map1); // Map {"info" => {name: "Jack", age: 26}} 1. 2. 3. 4. 5. 6. 也可以将对象或函数用作键。例如, // Map with object key let map2 = new Map(); let obj = {...
// s is 333. Note indexing is from zero, not oneletmyRecord={givenName:"Albert",familyName:"Einstein",age:33};// Create an "object" with three key:value pairsletname=myRecord.givenName;// name has string value "Albert"letdelete_file=false;// delete_file has a Boolean value "false...
var hamt = require('hamt'); // Keys can be any string and the map can store any value. var h = hamt.empty .set('key', 'value') .set('object', { prop: 1 }) .set('falsy', null); h.size === 0 h.has('key') === true h.has('falsy') === true h.get('key') =...
With the operator new we create an object of type String and define its value as in the second line of code. Both the first and the second lines of code have the same effect, so we’ll be using the first one in the next examples as it is simpler....
The key to this memoized version of the factorial function is the creation of a cache object. This object is stored on the function itself and is prepopulated with the two simplest factorials: 0 and 1. Before calculating a factorial, this cache is checked to see whether the calculation has...
function ArrayMap(f, receiver) { CHECK_OBJECT_COERCIBLE(this, "Array.prototype.map"); // Pull out the length so that modifications to the length in the // loop will not affect the looping and side effects are visible. var array = TO_OBJECT(this); var length = TO_LENGTH_OR_UINT32(...
(value.agency) already exists within our accumulator object. If not, we add it to the accumulator object and set its value to 1. If a key with the name of the current agencyalready exists within the accumulator object, we add 1 to its existing value. We return the accumulator object ...