console.log返回一个额外的未定义

Question

I am trying to understand .bind and made the following code:

a simply object:

person = {
    name:"Joe",
    surname:"Something",
    tool:"gun",
    action: function(){
        console.log("shoot my wife");
    }
}

a function:

function police(){
    console.log("You are under arrest, " + this.name + " " + this.surname);
}

and binding the person object to the police function

var newPolice = police.bind(person);

And finally I console log it:

console.log( newPolice() );

I do get the desired string ("You are under arrest, Joe Something") but I also get an undefined and I have no idea where it is coming from. (In the code it is the console.log(newPolice()) that generates the undefined)

Answer 1

This has nothing to do with bind .

When you call newPolice() it logs the result of this:

 console.log("You are under arrest, " + this.name + " " + this.surname); 

When you call console.log( newPolice() ); , you now have two console.log statements which, between them, log:

• The same thing as before
• The return value of newPolice

newPolice doesn't have a return statement, so it returns undefined .