这个JS代码在做什么

Question

What is that code doing?

var buf = new ArrayBuffer(fileContent.length);
var view = new Uint8Array(buf);
for (var i=0; i!=fileContent.length; ++i)
    view[i] = fileContent.charCodeAt(i) & 0xFF;

in context of function of FileSaver.js

saveAs(new Blob([buf],{type:""}), filename);

I cant get the entire goal of this code (except the last string, that saves the buf), cant get why are we changing view if we're saving buf , and how is view corresponds to the buf , and what is that fileContent.charCodeAt(i) & 0xFF command means?

Answer 1

charCodeAt(i) gets the i th character of the fileContent string, and returns its character code as a number. & 0xFF performs a binary AND operation between that number and the hexidecimal number 0xFF ; which masks it to the low-order 8 bits. Then this stores that 8-bit number into view[i] .

So this whole thing is essentially copying the string from fileContent to buf , but stripping off any high-order bits to get 8-bit characters.

The explicit masking here is not really necessary. Assigning to a Uint8Array automatically assigns the value modulo 256.