JavaScript Miscellaneous

Currying

Translates a function from callable as f(a, b, c) into callable as f(a)(b)(c).

Example

log(new Date(), "DEBUG", "some debug"); // log(a, b, c)

// can make a convenience function
let logNow = log(new Date()); // [HH:mm]

logNow("INFO", "message"); // [HH:mm] INFO message 

• logNow is log with fixed first argument, in other words “partially applied function” or “partial” for short.

  Advanced curry implementation ??

Reference Type

The value of Reference Type is a three-value combination (base, name, strict), where:

1. base is the object.
2. name is the property name.
3. strict is true if use strict is in effect.

• The result of a property access user.hi is not a function, but a value of Reference Type.

strict mode
// Reference Type value of `user.hi`
(user, "hi", true)

hi = user.hi 
// discards the reference type as a whole, takes the value of this function and passes it on.
// So any further operation “loses” `this`

• Reference type is a special “intermediary” internal type, with the purpose to pass information from dot . to calling parentheses ().

BigInt

BigInt is created by appending n to the end of an integer literal or by calling the function BigInt() that creates bigints from strings, numbers etc.

• All operations on bigints return bigints. 5n / 2n // 2
• We can’t mix bigints and regular numbers.
• The unary plus +value is not supported on bigints, we should use Number() to convert a bigint to a number.

Eval: run a code string

syntax

• eval is the result of the last statement.
• eval is executed in the current lexical environment, so it can see outer variables – That’s considered bad practice.
• In strict mode, eval has its own lexical environment. So functions and variables, declared inside eval, are not visible outside

let value = eval('let i = 0; ++i');
alert(value); // 1

Using eval

• Now, we can replace it with a modern language construct or a JavaScript Module.
• To eval the code in the global scope, use window.eval(code).
• Needs some data from the outer scope, use new Function('a', 'alert(a)') and pass it as arguments.