JavaScript syntax
part 15/31 · 107.4 KB total
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my_array = "We start at 11:30, 12:15 and 16:45".match(/\d\d:\d\d/g); // my_array==["11:30","12:15","16:45"];
Capturing groups
const myRe = /(\d{4}-\d{2}-\d{2}) (\d{2}:\d{2}:\d{2})/;
const results = myRe.exec("The date and time are 2009-09-08 09:37:08.");
if (results) {
console.log("Matched: " + results[0]); // Entire match
const my_date = results[1]; // First group == "2009-09-08"
const my_time = results[2]; // Second group == "09:37:08"
console.log(`It is ${my_time} on ${my_date}`);
} else console.log("Did not find a valid date!");
Function
Every function in JavaScript is an instance of the Function constructor:
// x, y is the argument. 'return x + y' is the function body, which is the last in the argument list.
const add = new Function('x', 'y', 'return x + y');
add(1, 2); // => 3
The add function above may also be defined using a function expression:
const add = function(x, y) {
return x + y;
};
add(1, 2); // => 3
In ES6, arrow function syntax was added, allowing functions that return a value to be more concise. They also retain the this of the global object instead of inheriting it from where it was called / what it was called on, unlike the function() {} expression.
const add = (x, y) => {return x + y;};
// values can also be implicitly returned (i.e. no return statement is needed)
const addImplicit = (x, y) => x + y;
add(1, 2); // => 3
addImplicit(1, 2) // => 3
For functions that need to be hoisted, there is a separate expression:
function add(x, y) {
return x + y;
}
add(1, 2); // => 3
Hoisting allows users to use the function before it is "declared":
add(1, 2); // => 3, not a ReferenceError
function add(x, y) {
return x + y;
}
A function instance has properties and methods.
function subtract(x, y) {
return x - y;
}
console.log(subtract.length); // => 2, arity of the function (number of arguments)
console.log(subtract.toString());
/*
"function subtract(x, y) {
return x - y;
}"
*/
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