如何将 class 方法放入变量中（javascript）

Question

I have an instance of mysql connection named db. db has a method named query to execute sql statement

example

db.query('SELECT * FROM user',[], callback)

To avoid repeating db.query I would like to do something like

const sqlCmd=db.query
sqlCmd('SELECT * FROM user',[], callback)

thanks in advance

Answer 1

You have to bind the call to the db object:

const sqlCmd=db.query.bind(db)

Answer 2

You can use the new Function() syntax, it's rarely used though:

const queryDB = new Function(`db.query('SELECT * FROM user',[], callback)`)
//then you can call it as:
queryDB()

you can also pass pass arguments as new Function(['argA', 'argB'], "function body")

Remember, [[Environment]] is set to reference not the current Lexical Environment, but the global one.

Answer 3

what you are trying to do here is called abstraction. Meaning you are adding a layer over the db class. So the simplest solution would be to create a module, add a method called query.

// let db = 'your sql db instance' 

 module.export.sqlCmd = db.query;

import this like

let sqlCmd = require('path to the above code')