Check if first letter of word is a capital letter

var word = "Someword";console.log( word[0] === word[0].toUpperCase() );

or

var word = "Someword";console.log( /[A-Z]/.test( word[0]) );

or

var word = "Someword";console.log( /^[A-Z]/.test( word) );

See toUpperCase() and test()

The other answers on this page are fine for strings that are known to only contain non-accented A-Z letters. If you can't guarantee this (e.g. user input), they may give unexpected results: false positives for uncapitalisable initials like "1940s" or "中文", or false negatives for accented or non-Roman capital initials like "Łukasz" or "Александра".

This variant returns true if the initial is any capital letter, and only if it's a capital letter:

function initialIsCapital( word ){  return word[0] !== word[0].toLowerCase();}

Use .charAt(0) instead of [0] if you need IE8 support. Which is faster varies between browsers.

This avoids two potential pitfalls with the other answers:

• Regexes using [A-Z] will fail to match accented and other similar non-A-Z capitalised letters such as in Åland (Scandinavian islands) and Łukasz (common Polish name), including capital letters in non-latin scripts such as Cyrillic or Greek (e.g. Александра).

• The approach using word[0] === word[0].toUpperCase(), will return true on words that start with non-letters, such as 1940s, 17th, 123reg (company name), abbreviations like 2mrw, or some words in some African languages, such as !xūún or ǂǐ-sì. It'll also treat any input from an alphabet that doesn't have capital letters as being capital letters (e.g. 中文).

Since this arbitrary-input-safe approach is just as simple and no less readable than the alternatives, it's probably better to use this even if you don't anticipate such exceptions.

Here's a quick test:

function a(word){  return word[0] !== word[0].toLowerCase();}function b(word){  return word[0] === word[0].toUpperCase();}function c(word){  return /^[A-Z]/.test( word );}function test(word, answer){  console.log( 'Should be '+answer+':',  a(word), b(word), c(word), '-------', word );}test( 'Łukasz', true ); // regex test fails, returns falsetest( 'Александра', true ); // regex test fails, returns falsetest( '1940s', false ); // .toUpperCase() test fails, returns truetest( '中文', false ); // .toUpperCase() test fails, returns truetest( 'ß', false ); // All pass on German "sharp S" that has no uppercasetest( 'Z̢̜̘͇̹̭a͎͚͔͕̩̬̭͈͞l̩̱̼̤̣g̲̪̱̼̘̜͟ợ̮̱͎̗̕ͅͅ', true ); // All pass. Phew, Zalgo not awakened