Seems that handling of "Defined Names" caused this issue.

Setter of definedNames model iterates over all definedNames ranges and as i can see initialize all named cells to their default values.

So in previously attached file there are several definedNames with a big range (e.g. $T$14:$T$1048576) so parser try to set default values for all cells in that range and spend a lot of time there and even more use a lot of memory (over 1.5 GB), which cause out of memory.

We have run into this also. I wonder if we really need to initialize the cells for a given "Defined Names", or they can just be left uninitialized.

@holm Don't know exactly, but we have patched this part of code and it works fine (note, that we do not use "defined names" feature and also only read files).

Here is the code that patch exceljs of version 1.1.2 to not initialize Defined Names if anyone interested.

import * as DefinedNames from "exceljs/dist/es5/doc/defined-names";

(function patchDefinedNames() {
    const desc = Object.getOwnPropertyDescriptor(DefinedNames.prototype, "model");
    Object.defineProperty(DefinedNames.prototype, "model", {
        get: desc.get,
        set: noop
    });
    
})();

function noop() {}