This time I bring you 9 very important usage skills (with code). What are the precautions for using JS? The following is a practical case, let’s take a look.
1. Delete the tail elements of the array
A simple way to clear or delete the tail elements of the array is to change the length of the array attribute value.
const arr = [11, 22, 33, 44, 55, 66]; // truncanting arr.length = 3; console.log(arr); //=> [11, 22, 33] // clearing arr.length = 0; console.log(arr); //=> [] console.log(arr[2]); //=> undefined
2. Use object destructuring to simulate named parameters
If you need to pass a series of optional options into a function as parameters, then you may tend to use a Object to define the configuration (Config).
doSomething({ foo: 'Hello', bar: 'Hey!', baz: 42 }); function doSomething(config) { const foo = config.foo !== undefined ? config.foo : 'Hi'; const bar = config.bar !== undefined ? config.bar : 'Yo!'; const baz = config.baz !== undefined ? config.baz : 13; // ... }
This is an old, but very effective method, which simulates named parameters in JavaScript. However, the way to handle config in doSomething is a bit cumbersome. In ES2015, you can use object destructuring directly.
function doSomething({ foo = 'Hi', bar = 'Yo!', baz = 13 }) { // ... }
If you want this parameter to be optional, that's easy too.
function doSomething({ foo = 'Hi', bar = 'Yo!', baz = 13 } = {}) { // ... }
3. Use object destructuring to process arrays
You can use the syntax of object destructuring to get the elements of the array:
const csvFileLine = '1997,John Doe,US,john@doe.com,New York'; const { 2: country, 4: state } = csvFileLine.split(',');
4 . Use range values in switch statements
You can use the following techniques to write switch statements that satisfy range values:
function getWaterState(tempInCelsius) { let state; switch (true) { case (tempInCelsius <= 0): state = 'Solid'; break; case (tempInCelsius > 0 && tempInCelsius < 100): state = 'Liquid'; break; default: state = 'Gas'; } return state; }
5. await multiple async functions
When using async/await, you can use Promise.all to await multiple async functions.
await Promise.all([anAsyncCall(), thisIsAlsoAsync(), oneMore()])
6. Create a pure object
You can create a 100% pure object, which does not inherit any properties or methods from Object ( For example, constructor, toString(), etc.).
const pureObject = Object.create(null); console.log(pureObject); //=> {} console.log(pureObject.constructor); //=> undefined console.log(pureObject.toString); //=> undefined console.log(pureObject.hasOwnProperty); //=> undefined
7. Format JSON code
JSON.stringify can not only characterize an object, but also format and output JSON objects.
const obj = { foo: { bar: [11, 22, 33, 44], baz: { bing: true, boom: 'Hello' } } }; // The third parameter is the number of spaces used to // beautify the JSON output. JSON.stringify(obj, null, 4); // =>"{ // => "foo": { // => "bar": [ // => 11, // => 22, // => 33, // => 44 // => ], // => "baz": { // => "bing": true, // => "boom": "Hello" // => } // => } // =>}"
8. Remove duplicate elements from an array
In ES2015, there is a set syntax. By using set syntax and the Spread operation, it is easy to remove duplicate elements:
const removeDuplicateItems = arr => [...new Set(arr)]; removeDuplicateItems([42, 'foo', 42, 'foo', true, true]); //=> [42, "foo", true]
9. Tiling multi-dimensional arrays
Using the Spread operation, it is easy To flatten nested multi-dimensional arrays:
const arr = [11, [22, 33], [44, 55], 66]; const flatArr = [].concat(...arr); //=> [11, 22, 33, 44, 55, 66]
Unfortunately, the above method only applies to two-dimensional arrays. However, with recursion, we can flatten nested arrays of arbitrary dimensions.
unction flattenArray(arr) { const flattened = [].concat(...arr); return flattened.some(item => Array.isArray(item)) ? flattenArray(flattened) : flattened; } const arr = [11, [22, 33], [44, [55, 66, [77, [88]], 99]]]; const flatArr = flattenArray(arr); //=> [11, 22, 33, 44, 55, 66, 77, 88, 99]
That’s it! I hope these tips can help you write more beautiful JS code! If that's not enough, you might as well use Fundebug as your assistant!
Featured Comments
Ethan B Martin: The writing of this switch is very clever, but I don’t recommend it. Please do not encourage developers to write JS code in this way. We once had an engineer write this, which later caused a lot of reading trouble during code review. Fortunately, we refactored it into more readable code in time. Let’s compare the difference between using switch and if:
function getWaterState1(tempInCelsius) { let state; switch (true) { case (tempInCelsius <= 0): state = 'Solid'; break; case (tempInCelsius < 100): state = 'Liquid'; break; default: state = 'Gas'; } return state; } function getWaterState2(tempInCelsius) { if (tempInCelsius <= 0) { return 'Solid'; } if (tempInCelsius < 100) { return 'Liquid'; } return 'Gas'; }
The second way of writing has several advantages:
A) The amount of code is smaller and more readable; B) You don’t need to declare a local variable, Readers won't have to keep track of how you changed this variable; C) switch(true) can be really confusing.
I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!
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