JavaScript Split And the Limit Property
One of the little used and known properties in JavaScript is the limit property in split. Limit returns the number of splits specified instead of all that can be found in a string. This is simpler than using regular expressions for simple operations like getting the first 2 lines of a string:
// From the command: df -h const commandResult = '' + 'Filesystem Size Used Avail Capacity iused ifree %iused Mounted on\n' + '/dev/disk1 233Gi 202Gi 30Gi 87% 2143375 4292823904 0% / \n' + 'devfs 186Ki 186Ki 0Bi 100% 644 0 100% /dev \n' + 'map -hosts 0Bi 0Bi 0Bi 100% 0 0 100% /net \n' + 'map auto_home 0Bi 0Bi 0Bi 100% 0 0 100% /home \n' + '/dev/disk0s3 620Mi 553Mi 66Mi 90% 71 4294967208 0% /Volumes/Recovery HD'; const parts = commandResult.split('\n', 2); // Print the first 2 lines console.info('Main system memory usage:\n', parts.join('\n')); // Filesystem Size Used Avail Capacity iused ifree %iused Mounted on // /dev/disk1 233Gi 202Gi 30Gi 87% 2143375 4292823904 0% /
Limit can also help with efficiency when parsing larger strings. For example, when parsing a file, it would be more efficient to extract the first 3 columns each time if a split with a limit of 3 was used:
const simulatedFileInput = '' + 'name,hp,weight,brand,drive\n' + 'miata,155,2400,mazda,RW\n' + 'elise,217,2000,lotus,RW\n' + '4C,237,2465,alpha romeo,RW'; var parseLine = function(line, index) { if (index > 0) { const parts = line.split(',', 3); return { name: parts[0], hp: parts[1], weight: parts[2] }; } return {}; } // Simulated line-by-line file stream const formattedData = simulatedFileInput.split('\n').map(parseLine); console.log(formattedData.slice(1));
The performance benefit can be seen with these JSPerf tests: https://jsperf.com/splitvslimitedsplit
Github Location: https://github.com/Jacob-Friesen/obscurejs/blob/master/2017/splitLimit.js
