Out of memory when concatinating strings

[espruino-discuss]

Posted at 2016-09-07 by ClearMemory041063

//strings.js

var A="1234567890";
var B=A;
console.log(B);console.log(B.length);
B=B+B;
console.log(B);console.log(B.length);
//out of memory if continued
//B=B+B;
//console.log(B);console.log(B.length);
//B=B+B;
//console.log(B);console.log(B.length);

B=A;
console.log(B);console.log(B.length);
B+=B;
console.log(B);console.log(B.length);
B+=B;
console.log(B);console.log(B.length);

Produces:

>echo(0);
1234567890
10
12345678901234567890
20
1234567890
10
12345678901234567890
20
ERROR: Out of Memory!
WARNING: Out of memory while appending to array
Execution Interrupted
=undefined
>

[espruino-discuss]

Posted at 2016-09-07 by JumJum

This works

var A="1234567890";
var B = A;
console.log(B.length,process.memory());
B+=A;
console.log(B.length,process.memory());
B+=A;
console.log(B.length,process.memory());

Looks like a problem with iterating through a string that is changed during iteration.

[gfwilliams]

Posted at 2016-09-07 by @gfwilliams

Interesting - thanks! I'll make an issue for this.

There was a post a few weeks ago where someone asked whether += was optimised to append. This looks like a side-effect of that optimisation.

[gfwilliams]

Posted at 2016-09-07 by @gfwilliams

Actually just fixed this - it was an easy tweak

[espruino-discuss]

Posted at 2016-09-07 by ClearMemory041063

Thanks Gordon, glad it was not a major rewrite.