Cannot read property 'x' of null

I get this error from this line: https://github.com/ericblade/quagga2/blob/156938f0a83935744c375ad235c2d16dd06fb3f7/src/locator/barcode_locator.js#L58

It looks like _patchSize can be null. I would create a PR to fix this but I’m not sure what you want to happen in the case that _patchSize is null.

[UziTech]

I queued the call to init so if the button is pressed three times in quick succession the first press will call init the second press will be queued to be called after the first finishes and the third press will replace the second in the queue since the first one hadn’t finished yet and cancel the second init. Once the first init is done I run stop since there is another one queued and the third press will be executed.

Here is the code I used to do that:

	// this function called on button press to start the stream
	async startCapture() {
		if (this.capturing) {
			this.stopCapture();
		}

		this.codes = [];
		try {
			const success = await this.queueInit(this.mapState());
			if (!success) {
				// another call queued while this one was queued
				return;
			}
		} catch (ex) {
			// stop stream if `init` finished but there is another call queued
			Quagga.stop();
			if (ex) {
				throw ex;
			}
			return;
		}
		// `init` finished and not overridden by another call
		Quagga.start();
		this.capturing = true;
	}

	callInit(init) {
		let failed = false;
		this.currInit = Quagga.init(init.config)
			.catch((ex) => {
				// throw `ex` but still call `nextInit` if exists
				init.reject(ex);
				failed = true;
			})
			.then(() => {
				if (this.nextInit) {
					// start next call to `init`
					if (!failed) {
						init.reject();
					}
					const nextInit = this.nextInit;
					this.nextInit = null;
					this.callInit(nextInit);
				} else {
					// last call so continue `startCapture`
					this.currInit = null;
					if (!failed) {
						init.resolve(true);
					}
				}
			});
	}

	queueInit(config) {
		let init;
		const promise = new Promise((resolve, reject) => {
			init = {
				config,
				resolve,
				reject,
			};
		});
		if (this.currInit) {
			if (this.nextInit) {
				// cancel current queued call
				this.nextInit.resolve(false);
			}
			this.nextInit = init;
		} else {
			// no current calls
			this.callInit(init);
		}
		return promise;
	}

[ericblade]

Good find. I’m still not sure if that should throw an error or if it should just pass all 0’s to the remainder of the function. I’ve been spending most of my programming time on other projects but I’ll do some thinking / research on this one and see what i can find. i know there’s already an issue to investigate spamming start/stop potentially causing problems, which this seems like it would be related to.

can you share what your fix in your code involved?