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Debugging Targeting expressions

How to enable ASRouter devtools​

  • In about:config, set browser.newtabpage.activity-stream.asrouter.devtoolsEnabled to true
  • Visit about:newtab#devtools-targeting to see the devtools (you need to copy-paste this manually to navigate).

Overview of ASRouter devtools​

Devtools image

Targeting​

Available targeting attributes are documented in firefox-source-docs.

Inside the textarea targeting expressions can be written and evaluated using the Evaluate button.

Targeting expressionStatusResultObservation
Correctly formatted JEXL expression
❌
✅		false
true		Depends on the truth value of the expression
Correctly formatted JEXL expression
referencing unknown variables		❌Empty resultUsing unknown variables is an error, result is neither true nor false
JEXL expression with syntax error❌<ERR_MSG>Full error message is shown

Builtin functions and examples​

The full list of available functions can be seen in FilterExpressions.sys.mjs.

A JEXL function is called using the | operator followed by the function name, example: [1,2,3]|length == 3.

  • Any preference can be read using |prefValue
  • An array of objects can be filtered by key value
topFrecentSites // An array of objects with `frequency` and `host` names

topFrecentSites[.frecency > 9000] // returns an array containing only those objects with frequency over 9000
  • [1,2,3] intersect [3,4,5] => [3]
  • [{a:1, type:"foo"}, {b:2, type:"bar"}]|mapToProperty("type") => ["foo", "bar"]
  • Date casting
// Is the profile older than 7 days
(currentDate | (date - profileAgeCreated)) / 86400000 > 7;
  • 1 in [1,2,3] => true
  • "JEXL expression"|regExpMatch("\w+") => ["JEXL"]