Here is a sample code for your reference, you can create a SharePoint site page and use Script Editor Web Part to embed it:
<script type="text/javascript" src="https://code.jquery.com/jquery-3.4.1.js"></script>
<script type="text/javascript">
function uploadDocument() {
if (!window.FileReader) {
alert("This browser does not support the HTML5 File APIs");
return;
}
var element = document.getElementById("uploadInput");
var file = element.files[0];
var parts = element.value.split("\\");
var fileName = parts[parts.length - 1];
var reader = new FileReader();
reader.onload = function (e) {
addItem(e.target.result, fileName);
}
reader.onerror = function (e) {
alert(e.target.error);
}
reader.readAsArrayBuffer(file);
function addItem(buffer, fileName) {
var call = uploadDocument(buffer, fileName);
call.done(function (data, textStatus, jqXHR) {
console.log(data);
alert("File Upload Successfully");
});
call.fail(function (jqXHR, textStatus, errorThrown) {
failHandler(jqXHR, textStatus, errorThrown);
});
}
function uploadDocument(buffer, fileName) {
var url = String.format(
"{0}/_api/Web/Lists/getByTitle('Documents')/RootFolder/Files/Add(url='{1}', overwrite=true)",
_spPageContextInfo.webAbsoluteUrl, fileName);
var call = jQuery.ajax({
url: url,
type: "POST",
data: buffer,
processData: false,
headers: {
Accept: "application/json;odata=verbose",
"X-RequestDigest": jQuery("#__REQUESTDIGEST").val()
}
});
return call;
}
function failHandler(jqXHR, textStatus, errorThrown) {
var response = JSON.parse(jqXHR.responseText);
var message = response ? response.error.message.value : textStatus;
alert("Call failed. Error: " + message);
}
}
</script>
<input type="file" id="uploadInput"/>
<input type="button" id="Upload" value="Upload" onclick="uploadDocument()"/>
