javascript error array creation

Question

this is the code

var xyzTris = [[[0,-3,4],[-2,0,4],[2,0,4]]];
console.log("zero: ",rdfTris);
var scrTris = [[[]]];
console.log("first: ",scrTris);
var rdfTris = [[[]]];
console.log("second: ",rdfTris);

What's strange is, the console out shows:

zero: undefined
first: Array [[[]]]
second: Array [[[0, -3, 4]]]

Anybody get why the rdfTris array is mal-defined?

I've tried all sorts of rearrangements, the parser just seems confused by rdfTris and xyzTris. I discovered this downstream when I was getting some weird array elements not defined later in the code. Stripped all that away to get to this.

Because you're logging rdfTris before assigning a value to it. Note, that only declarations are hoisted, not assignments. — Teemu
– Teemu, Commented Jun 4, 2018 at 15:11
where are you trying this .. just tried on chrome console the second array is coming fine , — Shyam Joshi
– Shyam Joshi, Commented Jun 4, 2018 at 15:12
Are the three letters before Tris meaningful, (xyz, scr, rdf)? Consider using longer more descriptive names to prevent confusions like this — IrkenInvader
– IrkenInvader, Commented Jun 4, 2018 at 15:15
To avoid this type of mistakes, you'd better use the let keyword, instead of var. — Marco Luzzara
– Marco Luzzara, Commented Jun 4, 2018 at 15:21
Thanks for input; the prefixes are incidental - xyz versus right-down-forward versus screen coordinates. I didn't want to edit anything lest I "fix" or change things somehow. I didn't use let over var because these are acting as global arrays. I got tired of passing references to every other function. Also, I realize the undefined is expected - what I am focused on is that once the rdf array IS defined, it takes on the value of the xyz array. Meanwhile, the scr array is initialized fine. — theDickChuck
– theDickChuck, Commented Jun 9, 2018 at 12:15

pseudological · Accepted Answer · 2018-06-04 15:12:28Z

1

You are logging the value of rdfTris on line 2, but you assign a value to rdfTris on line 5.

var xyzTris = [[[0,-3,4],[-2,0,4],[2,0,4]]];
console.log("zero: ",xyzTris);
var scrTris = [[[]]];
console.log("first: ",scrTris);
var rdfTris = [[[]]];
console.log("second: ",rdfTris);

The above should work as expected.

answered Jun 4, 2018 at 15:12

pseudological

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3 Comments

HMR Over a year ago

Hoisting is a strange thing, for example; you don't get rdfTris is not defined error even though you are using it before it is defined (suggests hoisting) but then it doesn't have a value even though you assign it a value when you define/declare it. This is because as Teemu suggested that declarations are hoisted but not assignments. Better answer would be to avoid var and stick to let if you plan to re assign and const if not.

pseudological Over a year ago

@HMR Totally agree, I think 'strange' is probably an understatement! I made the assumption that the poster was in an environment where const and let were unavailable. If they are, then definitely. I also think the suggestion by @IrkenInvader to use meaningful variable names would have helped!

HMR Over a year ago

JSLint used to complain if you did not declare all your variables at the start of the function so in an old environment I would suggest using that since the linter would point out that code as a possible mistake.

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