The key difference is that Objects only support string keys where as Maps support more or less any key type. Prior to ES6, when you need to map keys to values, you often use an object, because an object allows you to map a key to a value of any type. keys - Iterates the keys in the map; values - Iterates the values; entries - Iterates the key and values, giving you [key, value] arrays; As Nina notes, Maps also provide forEach, which loops through their contents giving the callback the value, key, and map as arguments.. Use the one appropriate for your use case. 1. Last updated Tuesday, April 28, 2020. Use Object.fromEntries(array) on the resulting array to turn it back into an object. Objects can retrieve keys, values, and entries by using the properties of the Object constructor. A property has a key (also known as “name” or “identifier”) before the colon ":" and a value to the right of it.. A lot of plain object’s issues (keys to string conversion, impossibility to use objects like keys, etc) are solved by Map object. ; The second one has the name "age" and the value 30.; The resulting user object can be imagined as a cabinet with two signed files labeled “name” and “age”. map. Note: map() does not execute the function for array elements without values.

If I do obj[123] = true and then Object.keys(obj) then I will get ["123"] rather than [123].A Map would preserve the type of the key and return [123] which is great. Returns the current angle of incidence of the map, in degrees from the viewport plane to the map plane. This is an index of all the classes, methods, and interfaces in the Maps JavaScript API version 3.41 (weekly channel). This reference is kept up to date with the latest changes to the API. Size Map 的键值对个数可以轻易地通过size 属性获取 Object 的键值对个数只能手动计算: 迭代: Map 是 iterable 的,所以可以直接被迭代。: 迭代一个Object需要以某种方式获取它的键然后才能迭代。: 性能: 在频繁增删键值对的场景下表现更好。 在频繁添加和删除键值对的场景下未作出优化。

The new Map() constructor accepts an iterable of entries. Definition and Usage. This post describes the use cases when it’s better to use maps instead of plain objects. Map is completely hash whereas Object is more than that.

Use Object.entries(obj) to get an array of key/value pairs from obj. With Object.entries, you can easily convert from Object to Map: The result will be 0 for imagery taken directly overhead or 45 for 45° imagery. Maps, on the other hand, have prototype methods that allow us to get the keys, values, and entries of the Map instance directly. Although Map tends to have more advantages over objects, at the end the day it depends on the kind of data being used and the operation needs to be performed. The first property has the name "name" and the value "John".
Google Maps JavaScript API V3 Reference.

While it may not have been there when the question was originally asked, it is now on the MDN page for Object.entries() under the heading Converting an Object to a Map which states: Converting an Object to a Map. Maps also allow you to use Objects as keys. If you’re starting in JavaScript, maybe you haven’t heard of .map(), .reduce(), and .filter().For me, it took a while as I had to support Internet Explorer 8 until a couple years ago. However, using an object as a map has some side effects: An object always has a default key like the prototype. Introduction to JavaScript Map object.

Map(0) {} Keys, Values, and Entries for Maps. In the user object, there are two properties:. 45° imagery is only available for satellite and hybrid map types, within some locations, and at some zoom levels.Note: This method does not return the value set by setTilt.
Objects lack many methods that exist for arrays, e.g. map, filter and others.