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Offload

Wolfram Kernel
WLJS
Execution environment
wljs-interpreter
Package
JerryI`Misc`WLJS`Transport`
Context

Holds (or offloads) an expression to be evaluated on frontend (WLJS)

Offload[expr_, opts___]

It has HoldFirst attribute.

info

Please, see the tutorial Dynamics

Options​

"Volatile"​

Blocks or allows dynamic updates. Only normal evaluation will be allowed if it is set to False. The default values is True

warning

In such case an expression will not be evaluated during the updates and will return undefined value. Use it only in constructions like CompoundExpression

"Static"​

Prevents or allows a parent instance to listen changes of an inner expression. The default value is False.

tip

The typical case scenario is you don't want to create extra bondings between an objects and other dynamic symbols.

For example

Line[{{0, a // Offload}, {1, a // Offload}}]

Line will be reevalauted 2 times instead of 1. 🔔 Since each instance of a causes the bond creation and reevaluation, once a has been changed.

Solution 1 👍🏼

Line[With[{p = a}, {{0, p}, {1, p}}] // Offload]

Solution 2 👍🏼

Line[{{0, a // Offload}, {1, Offload[a, "Static"->True]}}]

See also OffloadFromEventObject

Examples​

Symbols tracking and deferred evaluation​

Typical example for the dynamic evaluation

pts = RandomReal[{-1,1}, {64, 2}];
Graphics[{PointSize[0.02], Point[pts // Offload]}, ImageSize->500]
note

Try to update the page. Each time the distribution of points will be different

Now the symbol was actually evaluated on the frontend (browser/ client) using fetched data from the server.

And then, change the variable from the separate task

task = SetInterval[With[{},
  pts = (# + 0.001 Sum[
    (i - #)/(Norm[i - #]^3 + 0.1) - (i - #)/(Norm[i - #]^5 + 0.1)
  , {i, pts}]) &/@ pts;
], 100]

Don't forget to remove it afterwards

TaskRemove[task]

Force WL Kernel to offload an expression​

Looking back to the previous example, the function RandomReal implemented on both sides. If you offload it to the Point expression

Graphics[{PointSize[0.02], Point[RandomReal[{-1,1}, {64, 2}] // Offload]}]

Each time you load a notebook the distribution of the point will be different, since it reevaluate it on frontend's side each time.

Dev notes​

The actual implementation of the expression is extremely simple

SetAttributes[Offload, HoldFirst]
core.Offload = async (args, env) => {
	return await intepretate(args[0], env)
}
core.Offload.update = core.Offload
core.Offload.destroy = core.Offload

The difference from Hold is that it will not be affected by ReleaseHold.

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