Template strings

Template strings are string literals allowing embedded expressions. You can use multi-line strings and string interpolation features with them.

תחביר

`string text`

`string text line 1
 string text line 2`

`string text ${expression} string text`

tag `string text ${expression} string text`

תיאור

Template strings are enclosed by the back-tick (` `) (grave accent) character instead of double or single quotes. Template strings can contain place holders. These are indicated by the Dollar sign and curly braces (${expression}). The expressions in the place holders and the text between them get passed to a function. The default function just concatenates the parts into a single string. If there is an expression preceding the template string (tag here),  the template string is called "tagged template string". In that case, the tag expression (usually a function) gets called with the processed template string, which you can then manipulate before outputting.

Multi-line strings

Any new line characters inserted in the source are part of the template string. Using normal strings, you would have to use the following syntax in order to get multi-line strings:

console.log("string text line 1\n"+
"string text line 2");
// "string text line 1
// string text line 2"

To get the same effect with multi-line strings, you can now write:

console.log(`string text line 1
string text line 2`);
// "string text line 1
// string text line 2"

Expression interpolation

In order to embed expressions within normal strings, you would use the following syntax:

var a = 5;
var b = 10;
console.log("Fifteen is " + (a + b) + " and\nnot " + (2 * a + b) + ".");
// "Fifteen is 15 and
// not 20."

Now, with template strings, you are able to make use of the syntactic sugar making substitutions like this more readable:

var a = 5;
var b = 10;
console.log(`Fifteen is ${a + b} and\nnot ${2 * a + b}.`);
// "Fifteen is 15 and
// not 20."

Tagged template strings

A more advanced form of template strings are tagged template strings. With them you are able to modify the output of template strings using a function. The first argument contains an array of string literals ("Hello " and " world" in this example). The second, and each argument after the first one, are the values of the processed (or sometimes called cooked) substitution expressions ("15" and "50" here). In the end, your function returns your manipulated string. There is nothing special about the name tag in the following example. The function name may be anything you want.

var a = 5;
var b = 10;

function tag(strings, ...values) {
  console.log(strings[0]); // "Hello "
  console.log(strings[1]); // " world "
  console.log(values[0]);  // 15
  console.log(values[1]);  // 50

  return "Bazinga!";
}

tag`Hello ${ a + b } world ${ a * b}`;
// "Bazinga!"

Raw strings

The special raw property, available on the first function argument of tagged template strings, allows you to access the raw strings as they were entered.

function tag(strings, ...values) {
  console.log(strings.raw[0]); 
  // "string text line 1 \\n string text line 2"
}

tag`string text line 1 \n string text line 2`;

In addition, the String.raw() method exists to create raw strings just like the default template function and string concatenation would create.

String.raw`Hi\n${2+3}!`;
// "Hi\\n5!"

Security

Template strings MUST NOT be constructed by untrusted users, because they have access to variables and functions.

`${console.warn("this is",this)}`; // "this is" Window

let a = 10;
console.warn(`${a+=20}`); // "30"
console.warn(a); // 30

Specifications

Browser compatibility

See also

• String
• String.raw()
• Lexical grammar
• Template-like strings in ES3 compatible syntax
• "ES6 in Depth: Template strings" on hacks.mozilla.org