Destroyer catches up to polymerase

[ghost]

Test device:

MacBook Air (13-inch, Early 2015)

Operating System:

macOS Sierra Version 10.12.6 (16G29)

Browser:

Chrome Version 61.0.3163.100 (Official Build) (64-bit)

Problem description:

If the destroyer catches up to the polymerase, the expression screen stops working. You can't interact with anything in the expression screen. You can click on the other screens and sometimes you can interact with things, and sometimes you can't. Once you've selected another screen, you can't go back to the expression screen. This is for phetsims/QA/issues/58. Found this issue while looking at phetsims/gene-expression-essentials/issues/24.

gene-expression-essentials_en.html:990 Uncaught TypeError: Cannot read property 'add' of undefined
    at e.addLength (gene-expression-essentials_en.html:990)
    at e.step (gene-expression-essentials_en.html:990)
    at e.step (gene-expression-essentials_en.html:990)
    at e.step (gene-expression-essentials_en.html:990)
    at gene-expression-essentials_en.html:990
    at Array.forEach (<anonymous>)
    at e.forEach (gene-expression-essentials_en.html:990)
    at e.step (gene-expression-essentials_en.html:990)
    at e.stepSimulation (gene-expression-essentials_en.html:990)
    at e.runAnimationLoop (gene-expression-essentials_en.html:990)

Steps to reproduce:

1. Go to expression screen.
2. Go to third gene.
3. Add positive transcription factors.
4. Add polymerase.
5. Quickly add destroyer.

Screenshots:

Troubleshooting information (do not edit):

Name: ‪Gene Expression Essentials‬ URL: https://www.colorado.edu/physics/phet/dev/html/gene-expression-essentials/1.0.0-dev.13/gene-expression-essentials_en.html Version: 1.0.0-dev.13 2017-10-25 21:56:59 UTC Features missing: touch User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36 Language: en-US Window: 1438x656 Pixel Ratio: 1/1 WebGL: WebGL 1.0 (OpenGL ES 2.0 Chromium) GLSL: WebGL GLSL ES 1.0 (OpenGL ES GLSL ES 1.0 Chromium) Vendor: WebKit (WebKit WebGL) Vertex: attribs: 16 varying: 15 uniform: 1024 Texture: size: 16384 imageUnits: 16 (vertex: 16, combined: 80) Max viewport: 16384x16384 OES_texture_float: true Dependencies JSON: {"assert":{"sha":"928741cf","branch":"master"},"axon":{"sha":"80b60293","branch":"master"},"babel":{"sha":"ce29f350","branch":"master"},"brand":{"sha":"cfca902d","branch":"master"},"chipper":{"sha":"6b338220","branch":"master"},"dot":{"sha":"85ef2bbf","branch":"master"},"gene-expression-essentials":{"sha":"a8b7efc7","branch":"master"},"joist":{"sha":"eb3a1951","branch":"master"},"kite":{"sha":"2c921cba","branch":"master"},"phet-core":{"sha":"c30d15ed","branch":"master"},"phetcommon":{"sha":"b13138d2","branch":"master"},"query-string-machine":{"sha":"c74e454e","branch":"master"},"scenery":{"sha":"92a2872d","branch":"master"},"scenery-phet":{"sha":"d394b9df","branch":"master"},"sherpa":{"sha":"0d590744","branch":"master"},"sun":{"sha":"99a0abef","branch":"master"},"tandem":{"sha":"c1e98f69","branch":"master"}}

[phet-steele]

Ribosomes can do this too.

[jbphet]

Fixed, will have this tested in next dev or RC version.

[phet-steele]

Looks fixed.