wkwebview 怎么下载网页中的blob形式的文件

Question

self.script = @"";

    self.script = @"var xhr = new XMLHttpRequest();";

    NSString* open = [NSString stringWithFormat:@"xhr.open('GET', '\%@', true);",[url absoluteString]];

    self.script = [self.script stringByAppendingString:open];

    self.script = [self.script stringByAppendingString:@"xhr.responseType = 'blob';"];

    self.script = [self.script stringByAppendingString:@"window.webkit.messageHandlers.readBlob.postMessage('making sure script called');"];

    self.script = [self.script stringByAppendingString:@"xhr.onload = function(e) { if (this.status == 200) { var blob = this.response; var reader = new window.FileReader(); reader.readAsBinaryString(blob); reader.onloadend = function() { window.webkit.messageHandlers.readBlob.postMessage(reader.result); }}};"];

    self.script = [self.script stringByAppendingString:@"xhr.send();"];

 

reader.onloadend  这个方法不执行，有知道怎么回事的吗，请教大神门