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JavaScript toLowerCase ExamplesTransform the cases of strings with the toLowerCase and toUpperCase functions.
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ToLowerCase. A letter can be in one of 2 states—uppercase or lowercase. Characters have cases. In JavaScript we can transform cases dynamically with toLowerCase and toUpperCase.
First example. Here is a simple example. We use the methods toUpperCase and toLowerCase—these are the same as ToUpper, ToLower, upper, lower, upcase and downcase methods in other languages.
Example In case you are wondering, here is how you can use toUpperCase and toLowerCase.
Original The original string we call these methods on is left unchanged and be used again.
Here We take a string in mixed case (title case) and transform it to uppercase and then to all lowercase.
JavaScript program that uses toUpperCase, toLowerCase
var color = "Blue"; // Create a copy of the string and uppercase it. // ... The original is left alone. var upper = color.toUpperCase(); console.log("BEFORE: " + color); console.log("AFTER (UPPER): " + upper); // Lowercase a string. var lower = upper.toLowerCase(); console.log("BEFORE: " + upper); console.log("AFTER (LOWER): " + lower);
BEFORE: Blue AFTER (UPPER): BLUE BEFORE: BLUE AFTER (LOWER): blue
Uppercase first. Here we have the string "cat" and we transform the string. We access the first letter with the index 0, and uppercase this entire string. Then we add the remaining part.
Tip This method works well on strings of 1 character or more. And it can be placed in a function for easier reuse.
JavaScript program that uppercases first letter
var animal = "cat"; // Uppercase first letter in a string. var uppercase = animal[0].toUpperCase() + animal.substring(1); console.log("RESULT: " + uppercase);
RESULT: Cat
Uppercase first, function. Here we introduce the upperFirst function. It tests the argument to see if it has a length of 1 or greater. And then it uppercases the first letter in the string.
Tip This function handles zero-length strings. For strings with an initial letter already uppercased, it changes nothing.
JavaScript program that uses function
function upperFirst(value) { if (value.length >= 1) { return value[0].toUpperCase() + value.substring(1); } return value; } // Test upperFirst on many strings. var values = ["cat", "", "c", "dog", "BIRD"]; for (var i = 0; i < values.length; i++) { console.log("STRING: " + values[i]); console.log("UPPERFIRST: " + upperFirst(values[i])); }
STRING: cat UPPERFIRST: Cat STRING: UPPERFIRST: STRING: c UPPERFIRST: C STRING: dog UPPERFIRST: Dog STRING: BIRD UPPERFIRST: BIRD
Uppercase all words. With an iterative algorithm, we can uppercase all words in a string. Here we loop over the characters in a string.
And On the first character, or a lowercase-range ASCII letter following a space, we append the uppercase form of the letter.
For other chars We just append the original character. The result is built up as we go a long, and returned in the final line.
JavaScript program that uppercases all words in string
function uppercaseAllWords(value) { // Build up result. var result = ""; // Loop over string indexes. for (var i = 0; i < value.length; i++) { // Get char code at this index. var code = value.charCodeAt(i); // For first character, or a lowercase range char following a space. // ... The value 97 means lowercase A, 122 means lowercase Z. if (i === 0 || value[i - 1] === " " && code >= 97 && code <= 122) { // Convert from lowercase to uppercase by subtracting 32. // ... This uses ASCII values. result += String.fromCharCode(code - 32); } else { result += value[i]; } } return result; } console.log("RESULT: " + uppercaseAllWords("welcome visitors, enjoy your stay"));
RESULT: Welcome Visitors, Enjoy Your Stay
For performance, we can avoid excessive string transformations. We can cache lowercase or uppercase forms, or store them directly in the JS source.
In lowercasing strings, we transform only certain characters. Things like numbers and spaces and punctuation are left alone. Often it is best to cache the required string in your JS source.
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