While following the introductory tutorial, I came across a certain line that is confusing:
db.on('error', console.error.bind(console, 'connection error:'));
You can find it in this guide.
Wouldn't it be simpler to just use
db.on('error', ()=>{
console.log('connection error:')
});
Also, where does the actual error information go?
Essentially, the bind function creates a new function with predetermined parameters based on the original function it is called upon.
The first parameter of bind holds special significance and will be further discussed. Additional parameters passed to bind are "baked in" to the resulting function.
Consider the function addTwoNumbers:
function addTwoNumbers(a, b) {
return a + b
}
As addTwoNumbers is a function object, we can utilize bind to create a new function by specifying parameters:
var addThree = addTwoNumbers.bind(null, 3) // null is used as the first parameter since "this" is not required
The newly created function addThree now only requires one argument and functions similarly to:
function addThree(b) {
return addTwoNumbers(3, b)
}
Therefore, calling addThree(4) would yield 7.
The initial param supplied to bind determines the value of this within the scope of the new function.
For instance, consider the following function:
function printTheValueOfThis() {
console.log(this)
}
var printHello = printTheValueOfThis.bind('hello')
printHello() // this will output "hello" to the console
Within your code snippet, the targeted function is console.log and the "error information" is bound as the second argument.
An alternate way to represent this concept is through:
db.on('error', (someUnusedArg, errorInfo) => {
console.log('connection error:', errorInfo)
});
Various resources discuss the bind function in depth. For further reading, you may explore: bind Method (Function)
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