Evaluate JavaScript in the page — pz

Evaluates expr in the page, optionally awaiting a returned promise, and returns the resulting value. This is paparazzi's equivalent of Playwright's page.evaluate() (and likewise Puppeteer and the CDP Runtime.evaluate). It 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_evaluate(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_evaluate(page, "document.querySelectorAll('.task').length")
#> [1] 7

# Arrays come back as lists
pz_evaluate(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_evaluate(page, "new Promise(resolve => setTimeout(() => resolve('done'), 100))")
#> [1] "done"
pz_close(page)