I have been trying to work out how to use typed array's in JavaScript but something just isn't clicking yet for me. I am not understand how to read/write to the "view" properly.
var a = 23453.342;
now let's say I want to store this in a Float64Array typed array
view[0] = ??? //how do I copy the bytes that represent variable a into here.
Also let's say I want to store the integer 123456 that is in JavaScript internally as a 64Bit float:
var i = 123456;
but I would like to store it as if it was really a 4 byte integer.
var buff = new ArrayBuffer(4);
var view = new UInt32Array(buff);
view[0] = ???; //how do i determine and write the 4 bytes that would represent the value of i.
Then also in both cases once I am able to write the data there how do I read it back into local variables in JavaScript.
When you create a TypedArray of a certain type, say Int8Array like this:
let my = new Int8Array(1);
and assign a value to it, like this:
my[0] = 123456;
a conversion based on the this table is performed. So, for Int8Array the method ToInt8 is used with the last steps being:
...
Let int8bit be int modulo 2^8.
If int8bit ≥ 2^7, return int8bit − 2^8, otherwise return int8bit.
So, if we run these steps
Let int8bit be 123456 modulo 2^8 // 64
64 < 2^7 -> return int8bit, which is 64
So 64 is what you should expect:
console.log(my[0]); // 64
If you're interested in the actual bits order, check this answer for the algorithm or this article for the details of floating point.