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blockFunction.js
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blockFunction.js
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/*
Block a function from being called by adding and removing any number of blocks.
Excellent for waiting on parallel asynchronous operations.
A blocked function starts out with exactly one block
Example usage:
http.createServer(function(req, res) {
var sendResponse = blockFunction(function() {
res.writeHead(204)
res.end()
})
var queries = parseQueries(req.url)
for (var i=0; i<queries.length; i++) {
sendResponse.addBlock()
handleQuery(queries[i]; function() {
sendResponse.removeBlock()
})
}
})
*/
module.exports = function blockFunction(fn) {
var numBlocks = 0
return {
addBlock:function() {
numBlocks++
return this
},
removeBlock:function() {
if (!fn) { throw new Error("Block removed after function was unblocked") }
if (!numBlocks) { throw new Error("Tried to remove a block that was never added") }
if (--numBlocks) { return }
fn(null)
delete fn
return this
},
fail:function(error) {
fn(error)
delete fn
return this
}
}
}