The filter() method in JavaScript is used to create a new array containing all passing test elements. 1. filter() does not modify the original array, but returns a new array that meets the conditional elements; 2. The basic syntax is array.filter((element) => { return condition; }); 3. You can filter the object array by attribute value, such as filtering users older than 30; 4. Support multi-condition filtering, such as meeting both age and name length conditions at the same time; 5. You can handle dynamic conditions and pass filter parameters into functions to achieve flexible filtering; 6. When using it, be careful to return boolean values ??to avoid returning empty arrays, and combine other methods to implement complex logic such as string matching.
In JavaScript, processing arrays is a very common task in daily development. If you have an array of objects and want to filter out objects that meet the conditions based on certain conditions, filter() method is a very practical tool.
What is filter()?
filter() is a built-in method of an array that creates a new array containing all elements that pass the test (that is, elements whose callback function returns true ). This method does not modify the original array, but returns a new array.
The basic syntax is as follows:
const newArray = array.filter((element) => {
return condition;
});How to filter an array of objects by attribute values
This is one of the most common usage scenarios. For example, you have a user list and you want to find users older than 30 years old.
Suppose your data structure looks like this:
const users = [
{ name: 'Alice', age: 28 },
{ name: 'Bob', age: 35 },
{ name: 'Charlie', age: 30 }
];You can write this way:
const adults = users.filter(user => user.age > 30);
The result is [ { name: 'Bob', age: 35 } ] .
- Note: The callback function in
filtermust return a boolean value. - If you forget to write
returnor the arrow function does not return implicitly, you may get an empty array.
How to do multi-condition filtering?
Sometimes you need to judge multiple conditions together. For example, you want to find users who are "ager than 30 and whose name length is more than 3".
You can write this way:
const filtered = users.filter(user => user.age > 30 && user.name.length > 3);
Or split the logic in a clearer way:
const filtered = users.filter(user => {
const oldEnough = user.age > 30;
const nameLong = user.name.length > 3;
return oldEnough && nameLong;
});This writing method is more suitable for judgment of complex conditions and is easier to debug.
How to deal with dynamic conditions?
Sometimes, the filtering conditions are not fixed, but may be input from users. At this time, you can wrap the conditions into variables or function parameters.
For example:
function filterByAge(users, minAge) {
return users.filter(user => user.age >= minAge);
}
const result = filterByAge(users, 30);This allows users to be flexibly screened according to different minimum ages.
You can also expand to multiple dynamic parameters:
function filterUsers(users, minAge, maxAge) {
return users.filter(user => user.age >= minAge && user.age <= maxAge);
}Tips and FAQs
-
filter()returns a new array and will not change the original array. - If no elements satisfy the condition, an empty array is returned, not
undefined. - Don't forget to write
returnin the callback function, especially when using{}. - You can use
includes(),toLowerCase()and other methods to make string matching, such as searching for usernames to include a certain keyword.
// Find the user whose name contains "a" (case insensitive) users.filter(user => user.name.toLowerCase().includes('a'));
Basically these are the operations. Although it seems simple, it can meet many practical needs in combination. Just remember the core logic: items that return true will be retained.
The above is the detailed content of Filtering an Array of Objects in JavaScript. For more information, please follow other related articles on the PHP Chinese website!
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