Xjyuk

At the moment I have this:

function getValue(str)

	let result = 0;
	
	var regex = /(d+[a-z]+)/g;
	match = regex.exec(str);

	while (match != null) 
	
		var match_str 	= match[0];
		var last_char 	= match_str[match_str.length-1];

		if ( last_char == 'h' )
			result += parseInt(match_str) * 3600;
		if ( last_char == 'm' )
			result += parseInt(match_str) * 60;
		if ( last_char == 's' )
			result += parseInt(match_str);

		match = regex.exec(str);
	

	return result;


console.log( getValue("4h12m32s") );

It feels quite clumsy though. Also checking invalid values like 4hs feels difficult.

Is there any clever trick for something similar?

• 
  getValue(str) is such a vague name for the function and its parameter, it could mean anything! Furthermore, "get" implies that this is a getter function that retrieves something, which is not the case.


• Your regex is ineffective. Capturing parentheses could be useful, but you didn't actually use them right, such that you ended up having to pass a dirty string to parseInt() and extract the last character the harder way.


• You neglected to scope match, such that it acts as a global variable. The regex-matching statement is written twice; the assignment could be done within the loop condition instead.


• The if statements should be an if-else chain, since the conditions are mutually exclusive. However, since the branches are all so similar, a lookup table would be more elegant.

function durationSeconds(timeExpr)

	var units = 'h': 3600, 'm': 60, 's': 1;
	var regex = /(d+)([hms])/g;

	let seconds = 0;
	var match;
	while ((match = regex.exec(timeExpr))) 
	
		seconds += parseInt(match[1]) * units[match[2]];
	

	return seconds;


console.log( durationSeconds("4h12m32s") );

Alternatively, if you expect that the units will be in the conventional order, you don't have to loop at all.

function durationSeconds(timeExpr)
 0)
	 + 60 * (parseInt(match[2]) 

console.log( durationSeconds("4h32s") );

Named Capture Groups

JavaScript RegExp has named capture groups that can make life a lot simpler when dealing with complicated RegExp. Combined with destructuring assignment you can extract the named hours minutes and seconds as follows.

function toSeconds(time) 
 const groups: h = 0, m = 0, s = 0 = /(?<h>d*)h(?<m>d*)m(?<s>d*)/i.exec(time);
 return h * 3.6e3 + m * 60 + s * 1; // * 1 to coerce s to Number

Missing digits are set to zero in the assignment defaults.

However this is limited to strings that have hours, minutes, and seconds in the correct order (hence no need to match the "s") and will throw an error if there is a problem.

A more robust solution

You can also reduce the array created by symbol.matchAll (it returns an iterator that you convert to an array via spread operator)

It RegExp[symbol.matchAll] is the same call as String.matchAll(RegExp)

To handle as many variations as possible you can convert the time string to lowercase, soak up white spaces, allow for fractions, multiple periods, and negative periods.

Using an IIF to wrap the periods constant via closure the function looks like

const toSeconds = (() => 
 const periods = h: 3600, m: 60, s: 1;
 return time => [.../(-*d*.*d*)W*([hms])/g[Symbol.matchAll](time.toLowerCase())]
 .reduce((time, [, digits, type]) => periods[type] * digits + time, 0);
)();

Or via the string

const toSeconds = (() => 
 const periods = h: 3600, m: 60, s: 1;
 return time => [...time.toLowerCase().matchAll(/(-*d*.*d*)W*([hms])/g)]
 .reduce((time, [, digits, type]) => periods[type] * digits + time, 0);
)();

The snippet below shows some of the results of a variety of inputs.

const toSeconds = (() => 
 const periods = h: 3600, m: 60, s: 1;
 return time => [.../(-*d*.*d*)W*([hms])/g[Symbol.matchAll](time.toLowerCase())]
 .reduce((time, [, digits, type]) =>periods[type] * digits + time, 0);
)();



"1h,1m,1s,1,,1s2m3h,3h2m1s,2H2M2S,1h 1H1s1 S1m1M,1.1s,1.2s,s,1h-5m,1 1s,hms"
 .split(",")
 .forEach(time => log(""" + time + "" =" , toSeconds(time)+" seconds"));
 
function log(...data) 
 document.body.appendChild(
 Object.assign(
 document.createElement("div"), textContent: data.join(" ")
 )
 )

BTW in Javascript we put...

• the opening { on the same line as the statement,


• use camelCase for naming.

And from many years of C style language experience I would advise you to always delimit statement blocks with eg Bad if (foo) bar = foo, Good if (foo) bar = foo