A bit of code to check the size limit of your browser's localStorage

localStorageSize.js

/*
    An over-engineered way to check the max window.localStorage size of your browser.
    To run the test, past this code into the console of any browser tab.
*/

function testStorage(size, progress) {
    localStorage.clear();
    let dummyData = "";

    for (let i=0; i<size; i++) {
        dummyData+="\x00";
    }
    document.getElementById("display").innerHTML = `Testing storage size of ${size} bytes<br><br>${asciiProgressBar(progress, 40)}`;
    
    try {
        localStorage.setItem("_", dummyData);
        return true;
    } catch (e) {
        return false;
    }
}

function sizeDescriptor(size) {
    const k = 1024;
    if (size >= k*k) {
        return (size/(k*k)).toFixed(1)+" MiB";
    }
    if (size >= k) {
        return (size/k).toFixed(1)+" KiB";
    }
    return size+" bytes";
}

function asciiProgressBar(progress, length) {
    let bar = "";

    for (let i=0; i<length; i++) {
        if (i/length >= progress) {
            bar+=".";
        } else {
            bar+="=";
        }
    }
    return "["+bar+"] "+Math.floor(progress*100)+"%";

}

function findMaxStorageCapacity() {
    let lowerBound = 0;
    let upperBound = 1;
    // find the order of magnitude of the max size
    for (let i=0; i<9; i++) {
        let size = Math.pow(10, i);

        if (testStorage(size)) {
            lowerBound = size;
        } else {
            upperBound = size;
            break;
        }
    }

    let iteration = 0;
    let predictedIterations = Math.floor(Math.log2(upperBound-lowerBound));
    let f = ()=>{
        iteration++;
        let medianPoint = Math.floor((lowerBound+upperBound)/2);
        let progress = iteration/predictedIterations;
        if (testStorage(medianPoint, progress)) {
            lowerBound = medianPoint;
        } else {
            upperBound = medianPoint;
        }

        if (upperBound-lowerBound <= 1) {
            
            document.getElementById("display").innerHTML = `localStorage max size: ${upperBound} bytes (${sizeDescriptor(upperBound)})`
        } else {
            setTimeout(f, 10);
        }
    };
    f();
}


document.head.innerHTML = `
<style>
body {
    font-family: monospace;
    background-color: #161E20;
    color: #EBEEF7;
    padding: 20px;
}
</style>
`;
document.body.innerHTML = `
<h1>localStorage test</h1>
<div style="opacity:0.5;">The page may become unresponsive while the test is running</div>
<br>
<div id="display" style="opacity:0.5;">Performing initial tests...</div>
`;

setTimeout(findMaxStorageCapacity,1);

localStorageSize.min.js

function testStorage(e,t){localStorage.clear();let o="";for(let t=0;t<e;t++)o+="\0";document.getElementById("display").innerHTML=`Testing storage size of ${e} bytes<br><br>${asciiProgressBar(t,40)}`;try{return localStorage.setItem("_",o),!0}catch(e){return!1}}function sizeDescriptor(e){const t=1024;return e>=t*t?(e/(t*t)).toFixed(1)+" MiB":e>=t?(e/t).toFixed(1)+" KiB":e+" bytes"}function asciiProgressBar(e,t){let o="";for(let n=0;n<t;n++)o+=n/t>=e?".":"=";return"["+o+"] "+Math.floor(100*e)+"%"}function findMaxStorageCapacity(){let e=0,t=1;for(let o=0;o<9;o++){let n=Math.pow(10,o);if(!testStorage(n)){t=n;break}e=n}let o=0,n=Math.floor(Math.log2(t-e)),r=()=>{o++;let i=Math.floor((e+t)/2);testStorage(i,o/n)?e=i:t=i,t-e<=1?document.getElementById("display").innerHTML=`localStorage max size: ${t} bytes (${sizeDescriptor(t)})`:setTimeout(r,10)};r()}document.head.innerHTML="\n<style>\nbody {\n    font-family: monospace;\n    background-color: #161E20;\n    color: #EBEEF7;\n    padding: 20px;\n}\n</style>\n",document.body.innerHTML='\n<h1>localStorage test</h1>\n<div style="opacity:0.5;">The page may become unresponsive while the test is running</div>\n<br>\n<div id="display" style="opacity:0.5;">Performing initial tests...</div>\n',setTimeout(findMaxStorageCapacity,1);