Node.js sliced string memory - node.js

Question

I was trying:
r = [];
for (i = 0; i < 1e3; i++) {
a = (i+'').repeat(1e6);
r[i] = a.slice(64, 128);
}
and got an OutOfMemory. From here we see it's because all the as are kept in GC cuz a part of them are used.
How to make the slice don't keep the memory? I tried r[i]=''+a.slice(64, 128)+'' but still OOM. Do I have to a[64]+...+a[127] (loops also count as brute force)?
Is it so hard to slice and keep only necessary part of the old large string? The problem here only mentioned "copying every substring as a new string", but not "freeing part of the string remaining the necessary part assessible"

Answer 1

In this case it makes sense for the application code to be more aware of system constraints:
const r = [];
for (let i = 0; i < 1e3; ++i) {
const unitStr = String(i);
// choose something other than "1e6" here:
const maxRepeats = Math.ceil(128 / unitStr.length); // limit the size of the new string
// only using the last 64 characters...
r[i] = unitStr.repeat(maxRepeats).slice(64, 128);
}
...The application improvement is: to no longer construct 1000 strings of up to 3,000,000 bytes each when only 64 bytes are needed for each output string.
Your hardware and other constraints are not specified, but sometimes allowing the program more memory is appropriate:
node --max-old-space-size=8192 my-script.js
An analytic approach. Use logic to more precisely determine the in-memory state required for each working data chunk. With the constraints provided, minimize the generation of unneeded in-memory string data.
const r = new Array(1e3).fill().map((e,i) => outputRepeats(i));
function outputRepeats(idx) {
const OUTPUT_LENGTH = 128 - 64;
const unitStr = String(idx); // eg, '1', '40' or '286'
// determine from which character to start output from "unitStr"
const startIdxWithinUnit = (64 + 1) % unitStr.length; // this can be further optimized for known ranges of the "idx" input
// determine the approximate output string (may consume additional in-memory bytes: up to unitStr.length - 1)
// this can be logically simplified by unconditionally using a few more bytes of memory and eliminating the second arithmetic term
const maxOutputWindowStr = unitStr.repeat(Math.ceil(OUTPUT_LENGTH / unitStr.length) + Math.floor(Math.sign(startIdxWithinUnit)));
// return the exact resulting string
return maxOutputWindowStr.slice(startIdxWithinUnit, OUTPUT_LENGTH);
}