The
- Objects: Keys must be obtained and used to iterate over. Map: This is iterable, meaning we can directly iterate.
- Objects: The key can only be an integer, string, or symbol. Map: Key field can be of any data-type including objects and functions.
- Objects: Retrieving size is a manual process. Map: The size property hold this info.
- Objects: Iterating will not always return keys in the insertion order. Map: Remembers the insertion order, so iterating will always be in this order.
- Objects: Default keys can conflict with defined keys. Map: no default keys. All keys must be defined.
- Objects: Performance can struggle when frequently adding and removing key-value-pairs. Map: This is structured to perform than a standard object with frequent additions and removals.
// Set up an empty Map
let scores = new Map();
// Use .set(propName, value) to add to the map
scores.set("math", 90);
scores.set("physics", 95);
scores.set("chemistry", 80);
console.log(scores); // RESULT: Map(3) {"math" => 90, "physics" => 95, "chemistry" => 85}
// Use .get(propName) to retrieve specific values
console.log(scores.get("math")); // RESULT: 90
console.log(scores.get("physics")); // RESULT: 95
console.log(scores.get("chemistry")); // RESULT: 80
// Use size to check the size of the Map
console.log(scores.size); // RESULT: 3
// Use has to check a property exists in aMap
console.log(scores.has("english")); // RESULT: false
console.log(scores.has("math")); // RESULT: true
// Use .delete(propName) to remove a property
scores.delete("math");
console.log(scores.has("math")); // RESULT: false
// Use .clear() to remove all properties
scores.clear();
console.log(scores.size); // RESULT: 0
// SHORTCUT: Set up a Map with data
let scores = new Map([
["math", 90],
["physics", 95],
["chemistry", 85],
]);
console.log(scores); // RESULT: Map(3) {"math" => 90, "physics" => 95, "chemistry" => 85}
// Looping the a Map using a for...of loop with .get()
for (let key of scores.keys()) {
console,
log(key);
console.log(scores.get(key));
}
// RESULT: "math"
// 90
// "physics"
// 95
// "chemistry"
// 85
// .values() can be used to get only the values while iterating through a Map
for (let theValue of scores.values()) {
console.log(theValue);
}
// RESULT: 90
// 95
// 85
// .entries() can be used to get each key-value pair as an independent array
for (let theEntry of scores.entries()) {
console.log(theEntry[0], theEntry[1]);
}
// RESULT: "math" 90
// "physics" 95
// "chemistry" 85
// .entries() can also setup with the initial variable as the array
for (let [key, value] of scores.entries()) {
console.log(key, value);
}
// RESULT: "math" 90
// "physics" 95
// "chemistry" 85
