ECMAScript 2017
New Features in JavaScript 2017
| Feature | Description | |
|---|---|---|
| String padStart() | Pads the beginning of a string | |
| String padEnd() | Pads the end of a string | |
| Object entries() | Returns an array of the key/value pairs of an object | |
| Object values() | Returns an array of the values of an object | |
| async and await | Simplifies the handling of promises | |
| Trailing Commas | Allows trailing commas where a comma-separated list of values is accepted | |
| getOwnProperty Descriptors |
Returns an object containing all own property descriptors of an object |
Browser Support
JavaScript 2017 is supported in all modern browsers since September 2017:
| Chrome 58 |
Edge 15 |
Firefox 52 |
Safari 11 |
Opera 45 |
| Apr 2017 | Apr 2017 | Mar 2017 | Sep 2017 | May 2017 |
JavaScript String Padding
ECMAScript 2017 added two string methods to JavaScript: padStart()
and padEnd() to support padding at the beginning and at the end of a string.
Examples
let text = "5";
text = text.padStart(4,0);
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let text = "5";
text = text.padEnd(4,0);
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JavaScript Object Entries
ECMAScript 2017 added the Object.entries() method to objects.
Object.entries() returns an array of the key/value pairs in an object:
Example
const person = {
firstName : "John",
lastName : "Doe",
age : 50,
eyeColor : "blue"
};
let text = Object.entries(person);
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Object.entries() makes it simple to use objects in loops:
Example
const fruits = {Bananas:300, Oranges:200, Apples:500};
let text = "";
for (let [fruit, value] of Object.entries(fruits)) {
text += fruit + ": " + value + "<br>";
}
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Object.entries() also makes it simple to convert objects to maps:
Example
const fruits = {Bananas:300, Oranges:200, Apples:500};
const myMap = new Map(Object.entries(fruits));
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JavaScript Object Values
Object.values() is similar to Object.entries(),
but returns a single dimension array of the object values:
Example
const person = {
firstName : "John",
lastName : "Doe",
age : 50,
eyeColor : "blue"
};
let text = Object.values(person);
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JavaScript Async Functions
Waiting for a Timeout
async function myDisplay() {
let myPromise = new Promise(function(myResolve, myReject) {
setTimeout(function() { myResolve("I love You !!"); }, 3000);
});
document.getElementById("demo").innerHTML = await myPromise;
}
myDisplay();
JavaScript Trailing Commas
JavaScript allows trailing commas wherever a comma-separated list of values is accepted.
In Array and Object Literals, Function Calls, Parameters, Imports and Exports.
Example
function myFunc(x,,,) {};
const myArr = [1,2,3,4,,,];
const myObj = {fname: John, age:50,,,};
