
Run Scripts
🤖/script/run runs scripts in Assemblies.
This Robot allows you to run arbitrary JavaScript
as part of the
Assembly execution process. The Robot is invoked automatically when
there are Assembly Instructions containing ${...}
:
[
{
"robot": "/image/resize",
"width": "${Math.max(file.meta.width, file.meta.height)}"
}
]
You can also invoke this Robot directly, leaving out the ${...}
:
[
{
"robot": "/script/run",
"script": "Math.max(file.meta.width, file.meta.height)"
}
]
For more information, see Dynamic Evaluation.
Parameters
-
use
String / Array of Strings / ObjectrequiredSpecifies which Step(s) to use as input.
-
You can pick any names for Steps except
":original"
(reserved for user uploads handled by Transloadit) -
You can provide several Steps as input with arrays:
"use": [ ":original", "encoded", "resized" ]
💡 That’s likely all you need to know about
use
, but you can view advanced use cases:› Advanced use cases
-
Step bundling. Some Robots can gather several Step results for a single invocation. For example, 🤖/file/compress would normally create one archive for each file passed to it. If you'd set
bundle_steps
to true, however, it will create one archive containing all the result files from all Steps you give it. To enable bundling, provide an object like the one below to theuse
parameter:"use": { "steps": [ ":original", "encoded", "resized" ], "bundle_steps": true }
This is also a crucial parameter for 🤖/video/adaptive, otherwise you'll generate 1 playlist for each viewing quality.
Keep in mind that all input Steps must be present in your Template. If one of them is missing (for instance it is rejected by a filter), no result is generated because the Robot waits indefinitely for all input Steps to be finished.Here’s a demo that showcases Step bundling.
-
Group by original. Sticking with 🤖/file/compress example, you can set
group_by_original
totrue
, in order to create a separate archive for each of your uploaded or imported files, instead of creating one archive containing all originals (or one per resulting file). This is important for for 🤖/media/playlist where you'd typically set:"use": { "steps": [ "segmented" ], "bundle_steps": true, "group_by_original": true }
-
Fields. You can be more discriminatory by only using files that match a field name by setting the
fields
property. When this array is specified, the corresponding Step will only be executed for files submitted through one of the given field names, which correspond with the strings in thename
attribute of the HTML file input field tag for instance. When using a back-end SDK, it corresponds withmyFieldName1
in e.g.:$transloadit->addFile('myFieldName1', './chameleon.jpg')
.This parameter is set to
true
by default, meaning all fields are accepted.Example:
"use": { "steps": [ ":original" ], "fields": [ "myFieldName1" ] }
-
Use as. Sometimes Robots take several inputs. For instance, 🤖/video/merge can create a slideshow from audio and images. You can map different Steps to the appropriate inputs.
Example:
"use": { "steps": [ { "name": "audio_encoded", "as": "audio" }, { "name": "images_resized", "as": "image" } ] }
Sometimes the ordering is important, for instance, with our concat Robots. In these cases, you can add an index that starts at 1. You can also optionally filter by the multipart field name. Like in this example, where all files are coming from the same source (end-user uploads), but with different
<input>
names:Example:
"use": { "steps": [ { "name": ":original", "fields": "myFirstVideo", "as": "video_1" }, { "name": ":original", "fields": "mySecondVideo", "as": "video_2" }, { "name": ":original", "fields": "myThirdVideo", "as": "video_3" } ] }
For times when it is not apparent where we should put the file, you can use Assembly Variables to be specific. For instance, you may want to pass a text file to 🤖/image/resize to burn the text in an image, but you are burning multiple texts, so where do we put the text file? We specify it via
${use.text_1}
, to indicate the first text file that was passed.Example:
"watermarked": { "robot": "/image/resize", "use" : { "steps": [ { "name": "resized", "as": "base" }, { "name": "transcribed", "as": "text" }, ], }, "text": [ { "text" : "Hi there", "valign": "top", "align" : "left", }, { "text" : "From the 'transcribed' Step: ${use.text_1}", "valign" : "bottom", "align" : "right", "x_offset": 16, "y_offset": -10, } ] }
-
-
script
String⋅ example:"Math.max(min, file.meta.width)"
requiredA string of JavaScript to evaluate. It has access to all JavaScript features available in a modern browser environment.
The script is expected to return a
JSON.stringify
-able value in the same tick, so noawait
or callbacks are allowed (yet).If the script does not finish within 1000ms it times out with an error. The return value or error is exported as
file.meta.result
. If there was an error,file.meta.isError
istrue
. Note that the Assembly will not crash in this case. If you need it to crash, you can check this value with a 🤖/file/filter Step, settingerror_on_decline
totrue
.You can check whether evaluating this script was free by inspecting
file.meta.isFree
. It is recommended to do this during development as to not see sudden unexpected costs in production.
Related blog posts
- Introducing the /script/run Robot December 15, 2021
- Transloadit Milestones of 2021 January 31, 2022
- Generate a preview of a website using Transloadit CDN May 11, 2022