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Once the page is loaded, stream the update info into the page. — prototype.js
Literal
Page [subject-が] be-loaded-[if/when-たら] update-info [object-を] page-inside [into-に] pour-in. prototype.js
A technical note, probably a comment in or about JavaScript (prototype.js is a once-popular JS library). The conditional ~たら attached to the passive 読み込まれた means 'once / after loading is complete.' 流し込む is a compound verb: 流す ('flow, cause to flow') + 込む ('into'), meaning 'pour into,' 'stream into,' or in programming contexts 'inject' or 'feed' data into a container. The terse, fragmentary style (no copula, no desu/masu) is typical of technical memos and documentation.