Why can only use the access mode [] for traversal?

var xiaoming = {
    name: 'Ming'.birth: 1990.school: 'No.1 Middle School'.height: 1.70.weight: 65.score: null
};
for(var i in xiaoming){
    console.log(`${i}:${xiaoming[i]}`);
}

// The output will be normalName: xiao Ming birth:1990
 school:No1. Middle School
 height:1.7
 weight:65
 score:nullIf it isfor(var i in xiaoming){
    console.log(`${i}:${xiaoming.i}`);
}

// The output is
name:undefined
 birth:undefined
 school:undefined
 height:undefined
 weight:undefined
 score:undefined
Copy the code

This result is due to the fact that the preceding I normally iterates through the object’s property name and prints it. The following xiaoming. I is actually the I property of the object called xiaoming, so undefined is output.

If you add I to a variable, you’ll see that the output will print the value of the I property seven times.