未捕获的语法错误：JSON 输入的意外结束：在 JSON.parse（<anonymous> )</anonymous>

Question

it throws error when I try to parse localStorage['highscores"]

if (localStorage["highscores"] == undefined) {
    localStorage["highscores"] = [];
}
var highscores = JSON.parse(localStorage["highscores"]) || [];

I have not defined localStorage['highscores"] so I try to check it and if it is undefined define it, bcs if it is full I want to save it's information in localStorage['highscores"] and add more information too.

any ideas?

Answer 1

Local Storage may only hold strings. When you set non-strings to it, it'll be coerced to a string.

When arrays are converted to strings, .join(',') is called on the string. The empty array will be converted into the empty string:

 console.log(String([]) === '');

Which is not JSON-parseable.

Save the JSON-stringified version of the empty array instead.

if (localStorage.highscores === undefined) {
    localStorage.highscores = '[]';
}

or

if (localStorage.highscores === undefined) {
    localStorage.highscores = JSON.stringify([]);
}

When in doubt, always use JSON.stringify / JSON.parse when transferring to and from Local Storage.