Evaluate JavaScript in the page

Evaluates expr in the page, optionally awaiting a returned promise, and returns the resulting value. This is the primitive all element work uses, and an escape hatch for one-off scripts. Unlike most pz_*() functions it ends the chain: it returns the value, not the context.

Usage

pz_js(ctx, expr, ..., await = TRUE, timeout = NULL)

Arguments

ctx

A paparazzi context.

expr

A string of JavaScript to evaluate.

...

Checked empty; reserved for future use.

await

Await a promise returned by expr before returning its value.

timeout

Seconds before the evaluation fails; NULL uses the session default.

Value

The value produced by expr (converted to R), or NULL.

Examples

page <- pz_open(pz_example("tasks"))
pz_js(page, "document.querySelectorAll('.task').length")
#> [1] 7

# Arrays come back as lists
pz_js(page, "[...document.querySelectorAll('.task-priority')].map(el => el.textContent)")
#> [[1]]
#> [1] "high"
#> 
#> [[2]]
#> [1] "high"
#> 
#> [[3]]
#> [1] "normal"
#> 
#> [[4]]
#> [1] "low"
#> 
#> [[5]]
#> [1] "normal"
#> 
#> [[6]]
#> [1] "low"
#> 
#> [[7]]
#> [1] "normal"
#> 

# Returned promises are awaited
pz_js(page, "new Promise(resolve => setTimeout(() => resolve('done'), 100))")
#> [1] "done"
pz_close(page)