javascript-common

The code in this package is common to be used in some my projects. Although for my projects, it may be useful for you. Things that can be imported from this package:

noop

It's a function that does nothing (() => {}). This function is often used as the default value for a variable whose function type. Instead of maintaining many copies, it's better to keep one copy in memory.

noChange

This function returns the parameter that is passed into it, no change (p => p). Like noop, this function is often used as the default value for a variable whose function type. Instead of maintaining many copies, it's better to keep one copy in memory.

emptyArray

This is a read-only empty array ([]). Read-only means we cannot add/remove an entry to/from it. It's useful for a initial value of a "state" variable whose array type. In "React" framework, it can be used as the parameter of React.useState hook function. If there are many array "state" variable, it's better to keep one copy in memory. It's safe to share among some "state" variables because an array "state" variable is considered to change if it's assigned to a different instance of array. So, we may not just call push method and re-assign it.

emptyObject

This is a read-only empty plain object ({}). Read-only means we cannot set/unset a property to/from it. It's useful for a initial value of a "state" variable whose type of a plain object. In "React" framework, it can be used as the parameter of React.useState hook function. If there are many object "state" variable, it's better to keep one copy in memory. It's safe to share among some "state" variables because an object "state" variable is considered to change if it's assigned to a different instance of object. So, we may not just set/unset a property and re-assign it.

emptyString

This is an empty string (""). An empty string is often used as the default value of a string variable.

extendObject(target, extObj)

It extends the object target by adding to it the new members (properties/methods) from the object extObj. It's like Object.assign(target, extObj), but different from Object.assign, when there are some the same members among target and extObj, it doesn't remove those members from target and replace them with the same ones from extObj. The original members still exist in target. This function is simply invoke Object.setPrototypeOf(extObj, target). If it's so simple, why do we need the wrapper function? It's because we need a static type checking. The type of the returned value should be the type which is combination between target's type and extObj's type.

<T extends object, P extends object>(target: T, extObj: P) => T & P

proxyObject(target, extObj, proxiedIfNotExist)

Similar to extendObject but it doesn't change the prototype of target. It utilizes a Proxy object. It's useful if target already has a prototype object.
Parameters:

• target
  The extended object
• extObj
  The object which has the extending members. It may be also a function with format target => extObj.
• proxiedIfNotExist
  If true then a member is read from extObj only if the member doesn't exist on target. By default, it's false.

proxyClass(Target, extObj, proxiedIfNotExist)

Similar to proxyObject but the first parameter is not an instance object, it's a class of target object. This function will create the target instance: const target = new Target(...args) and then call proxyObject. This function returns a Proxy object of the class, NOT proxy of the Target instance.