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Var s2 = new String('2 + 2') // creates a String objectĬonsole.log(eval(s1)) // returns the number 4Ĭonsole.log(eval(s2)) // returns the string "2 + 2"įor these reasons, code may break when it encounters String objects when it expects a primitive string instead, although generally authors need not worry about the distinction.Ī String object can always be converted to its primitive counterpart with the valueOf() method. For example: var s1 = '2 + 2' // creates a string primitive Primitives passed to eval are treated as source code String objects are treated as all other objects are, by returning the object. String primitives and String objects also give different results when using eval(). var s_prim = 'foo' Ĭonsole.log(typeof s_prim) // Logs "string"Ĭonsole.log(typeof s_obj) // Logs "object" In contexts where a method is to be invoked on a primitive string or a property lookup occurs, JavaScript will automatically wrap the string primitive and call the method or perform the property lookup. JavaScript automatically converts primitives to String objects, so that it's possible to use String object methods for primitive strings. String literals (denoted by double or single quotes) and strings returned from String calls in a non-constructor context (i.e., without using the new keyword) are primitive strings. (The same is true of Boolean and Numbers.)
Note that JavaScript distinguishes between String objects and primitive string values. Distinction between string primitives and String objects In JavaScript, you just use the less-than and greater-than operators: var a = 'a' Ī similar result can be achieved using the localeCompare() method inherited by String instances. (See fineProperty() for more information.) Comparing stringsĬ developers have the strcmp() function for comparing strings. The properties involved are neither writable nor configurable. The other way (introduced in ECMAScript 5) is to treat the string as an array-like object, where individual characters correspond to a numerical index: return 'cat' // returns "a"įor character access using bracket notation, attempting to delete or assign a value to these properties will not succeed. The first is the charAt() method: return 'cat'.charAt(1) // returns "a" There are two ways to access an individual character in a string. Some of the most-used operations on strings are to check their length, to build and concatenate them using the + and += string operators, checking for the existence or location of substrings with the indexOf() method, or extracting substrings with the substring() method. Strings are useful for holding data that can be represented in text form. Parameters thing Anything to be converted to a string. Or, using the String global object directly: String(thing) Since EcmaScript 6 String literals can also be so-called Template Strings: `hello world`īeside regular, printable characters, special characters can be encoded using escape notation: Code String literals take the forms: 'string text' The String global object is a constructor for strings, or a sequence of characters.
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