JSON-未捕获的TypeError：无法读取未定义的属性

Question

I want take some JSON values and make variable from them, but when I do it I get an error. In first stage JSON array is empty, thats why I used if != null , but even with filled array I get an error.

var tempJS=[];  
$("#sth td").each(function(){
    $this = $(this);
    tempJS.push({"COLOR":$this.attr("data-color"),});
});
console.log(JSON.stringify(tempJS));

if(tempJS!=null) var kolor=tempJS[c-1].COLOR;

Why is the last line giving me the following error:

Uncaught TypeError: Cannot read property 'COLOR' of undefined

Answer 1

If you try on the console:

[]==null
> false

you'll see that returns false . This means that if you check if the array equals null you will always get a false, and always run the code in the if statement.

You should do this instead:

if(tempJS.length) var kolor=tempJS[c-1].COLOR;

You don't need if(tempJS.length > 0) because every number is treated like true except 0 that means false .

Answer 2

A zero-length array is not same as null. Try testing if (tempJS.length > 0) ...