тип так
var pattern = /https?[^<]+/g
var data =`[Output] https://online.site.com/u/public/api/20171209-081351-999999999-verypdf.jpg<br>
[Output] http://online.site.com/u/public/api/20171209-081351-999999999-verypdf.jpg<br>
[Output] http://online.site.com/u/public/api/20171209-081351-999999999-verypdf.jpg<br>`
var arr = data.match(pattern)
alert(arr)