library("rjson")
fromJSON("[{'id': 18, 'name': 'Drama'}, {'id': 28, 'name': 'Action'}, {'id': 10749, 'name': 'Romance'}]")

js <- '[{
      "id": 14,
    "name": "Fantasy"
    }, {
    "id": 28,
    "name": "Action"
    }, {
    "id": 53,
    "name": "Thriller"
    }]'

## this is your invalid string
js <- "[{'id': 18, 'name': 'Drama'}, {'id': 28, 'name': 'Action'}, {'id': 10749, 'name': 'Romance'}]"

## convert it to a valid string
js <- gsub("QUUX", "'", gsub("'", '"', gsub('"', "QUUX", js)))

jsonlite::fromJSON(js)

#     id    name
#1    18   Drama
#2    28  Action
#3 10749 Romance

rjson::fromJSON(js)

[[1]]
[[1]]$id
[1] 18

[[1]]$name
[1] "Drama"


[[2]]
[[2]]$id
[1] 28

[[2]]$name
[1] "Action"


[[3]]
[[3]]$id
[1] 10749

[[3]]$name
[1] "Romance"