Javascript中的局部变量与全局变量

Question

I have this code in Javascript:

var words = [];

d3.json("myFile.json", function(data) {
    words = data.words;
    console.log(words);  //Log output to console
});

console.log(words);  //Log output to console

The first console.log(words); shows an array of seven objects. But the second console.log(words); shows an empty array. So it looks like words outside of the d3.json function is not the same as words inside that function.

I also have tried to use console.log(window.words); outside of the function and it still shows an empty array.

How can I get the data that I have read from myFile.json in the d3.json function, outside of that function?

Answer 1

d3.json is an asynchronous function. That means that the code you pass is not executed immediately, but as a callback after the request for the JSON file returns. That is, a network request is sent for the file, but the normal flow of execution continues.

The console.log(words); outside d3.json is simply executed before the call returns and the array is populated.