问题
Consider this code:
var age = 3;
console.log("I'm " + age + " years old!");
Are there any other ways to insert the value of a variable in to a string, apart from string concatenation?
回答1:
Since ES6, you can use template literals:
const age = 3
console.log(`I'm ${age} years old!`)P.S. Note the use of backticks: ``.
回答2:
tl;dr
Use ECMAScript 2015's Template String Literals, if applicable.
Explanation
There is no direct way to do it, as per ECMAScript 5 specifications, but ECMAScript 6 has template strings, which were also known as quasi-literals during the drafting of the spec. Use them like this:
> var n = 42;
undefined
> `foo${n}bar`
'foo42bar'
You can use any valid JavaScript expression inside the {}. For example:
> `foo${{name: 'Google'}.name}bar`
'fooGooglebar'
> `foo${1 + 3}bar`
'foo4bar'
The other important thing is, you don't have to worry about multi-line strings anymore. You can write them simply as
> `foo
... bar`
'foo\n bar'
Note: I used io.js v2.4.0 to evaluate all the template strings shown above. You can also use the latest Chrome to test the above shown examples.
Note: ES6 Specifications are now finalized, but have yet to be implemented by all major browsers.
According to the Mozilla Developer Network pages, this will be implemented for basic support starting in the following versions: Firefox 34, Chrome 41, Internet Explorer 12. If you're an Opera, Safari, or Internet Explorer user and are curious about this now, this test bed can be used to play around until everyone gets support for this.
回答3:
Douglas Crockford's Remedial JavaScript includes a String.prototype.supplant function. It is short, familiar, and easy to use:
String.prototype.supplant = function (o) {
return this.replace(/{([^{}]*)}/g,
function (a, b) {
var r = o[b];
return typeof r === 'string' || typeof r === 'number' ? r : a;
}
);
};
// Usage:
alert("I'm {age} years old!".supplant({ age: 29 }));
alert("The {a} says {n}, {n}, {n}!".supplant({ a: 'cow', n: 'moo' }));
If you don't want to change String's prototype, you can always adapt it to be standalone, or place it into some other namespace, or whatever.
回答4:
Word of caution: avoid any template system which does't allow you to escape its own delimiters. For example, There would be no way to output the following using the supplant() method mentioned here.
"I am 3 years old thanks to my {age} variable."
Simple interpolation may work for small self-contained scripts, but often comes with this design flaw that will limit any serious use. I honestly prefer DOM templates, such as:
<div> I am <span id="age"></span> years old!</div>
And use jQuery manipulation: $('#age').text(3)
Alternately, if you are simply just tired of string concatenation, there's always alternate syntax:
var age = 3;
var str = ["I'm only", age, "years old"].join(" ");
回答5:
Try sprintf. For example:
vsprintf('The first 4 letters of the english alphabet are: %s, %s, %s and %s', ['a', 'b', 'c', 'd']);
回答6:
You could use Prototype's template system if you really feel like using a sledgehammer to crack a nut:
var template = new Template("I'm #{age} years old!");
alert(template.evaluate({age: 21}));
回答7:
I use this pattern in a lot of languages when I don't know how to do it properly yet and just want to get an idea down quickly:
// JavaScript
var stringValue = 'Hello, my name is {name}. You {action} my {relation}.'
.replace(/{name}/g ,'Indigo Montoya')
.replace(/{action}/g ,'killed')
.replace(/{relation}/g,'father')
;
While not particularily efficient, I find it readable. It always works, and its always available:
' VBScript
dim template = "Hello, my name is {name}. You {action} my {relation}."
dim stringvalue = template
stringValue = replace(stringvalue, "{name}" ,"Luke Skywalker")
stringValue = replace(stringvalue, "{relation}","Father")
stringValue = replace(stringvalue, "{action}" ,"are")
ALWAYS
* COBOL
INSPECT stringvalue REPLACING FIRST '{name}' BY 'Grendel'
INSPECT stringvalue REPLACING FIRST '{relation}' BY 'Mother'
INSPECT stringvalue REPLACING FIRST '{action}' BY 'did unspeakable things to'
回答8:
You can do easily using ES6 template string and transpile to ES5 using any available transpilar like babel.
const age = 3;
console.log(`I'm ${age} years old!`);
http://www.es6fiddle.net/im3c3euc/
回答9:
Try kiwi, a light-weight JavaScript module for string interpolation.
You can do
Kiwi.compose("I'm % years old!", [age]);
or
Kiwi.compose("I'm %{age} years old!", {"age" : age});
回答10:
If you want to interpolate in console.log output, then just
console.log("Eruption 1: %s", eruption1);
^^
Here, %s is what is called a "format specifier". console.log has this sort of interpolation support built-in.
回答11:
Here's a solution which requires you to provide an object with the values. If you don't provide an object as parameter, it will default to using global variables. But better stick to using the parameter, it's much cleaner.
String.prototype.interpolate = function(props) {
return this.replace(/\{(\w+)\}/g, function(match, expr) {
return (props || window)[expr];
});
};
// Test:
// Using the parameter (advised approach)
document.getElementById("resultA").innerText = "Eruption 1: {eruption1}".interpolate({ eruption1: 112 });
// Using the global scope
var eruption2 = 116;
document.getElementById("resultB").innerText = "Eruption 2: {eruption2}".interpolate();<div id="resultA"></div><div id="resultB"></div>回答12:
Expanding on Greg Kindel's second answer, you can write a function to eliminate some of the boilerplate:
var fmt = {
join: function() {
return Array.prototype.slice.call(arguments).join(' ');
},
log: function() {
console.log(this.join(...arguments));
}
}
Usage:
var age = 7;
var years = 5;
var sentence = fmt.join('I am now', age, 'years old!');
fmt.log('In', years, 'years I will be', age + years, 'years old!');
回答13:
I can show you with an example:
function fullName(first, last) {
let fullName = first + " " + last;
return fullName;
}
function fullNameStringInterpolation(first, last) {
let fullName = `${first} ${last}`;
return fullName;
}
console.log('Old School: ' + fullName('Carlos', 'Gutierrez'));
console.log('New School: ' + fullNameStringInterpolation('Carlos', 'Gutierrez'));回答14:
Since ES6, if you want to do string interpolation in object keys, you will get a SyntaxError: expected property name, got '${' if you do something like:
let age = 3
let obj = { `${age}`: 3 }
You should do the following instead:
let obj = { [`${age}`]: 3 }
回答15:
Using template syntax fails in older browsers, important if you are creating HTML for public use. Using concatenation is tedious and hard to read, particularly if you have many or long expressions, or if you must use parentheses to handle mixtures of number and string items (both of which use the + operator).
PHP expands quoted strings containing variables and even some expressions using a very compact notation: $a="the color is $color";
In JavaScript, an efficient function can be written to support this: var a=S('the color is ',color);, using a variable number of arguments. While there is no advantage over concatenation in this example, when the expressions get longer this syntax may be clearer. Or one can use the dollar sign to signal the start of an expression using a JavaScript function, as in PHP.
On the other hand, writing an efficient workaround function to provide template-like expansion of strings for older browsers wouldn't be hard. Someone has probably done it already.
Finally, I imagine that sprintf (as in C, C++, and PHP) could be written in JavaScript, although it would be a little less efficient than these other solutions.
回答16:
Supplant more for ES6 version of @Chris Nielsen's post.
String.prototype.supplant = function (o) {
return this.replace(/\${([^\${}]*)}/g,
(a, b) => {
var r = o[b];
return typeof r === 'string' || typeof r === 'number' ? r : a;
}
);
};
string = "How now ${color} cow? {${greeting}}, ${greeting}, moo says the ${color} cow.";
string.supplant({color: "brown", greeting: "moo"});
=> "How now brown cow? {moo}, moo, moo says the brown cow."
回答17:
Custom flexible interpolation:
var sourceElm = document.querySelector('input')
// interpolation callback
const onInterpolate = s => `<mark>${s}</mark>`
// listen to "input" event
sourceElm.addEventListener('input', parseInput)
// parse on window load
parseInput()
// input element parser
function parseInput(){
var html = interpolate(sourceElm.value, undefined, onInterpolate)
sourceElm.nextElementSibling.innerHTML = html;
}
// the actual interpolation
function interpolate(str, interpolator = ["{{", "}}"], cb){
// split by "start" pattern
return str.split(interpolator[0]).map((s1, i) => {
// first item can be safely ignored
if( i == 0 ) return s1;
// for each splited part, split again by "end" pattern
const s2 = s1.split(interpolator[1]);
// is there's no "closing" match to this part, rebuild it
if( s1 == s2[0]) return interpolator[0] + s2[0]
// if this split's result as multiple items' array, it means the first item is between the patterns
if( s2.length > 1 ){
s2[0] = s2[0]
? cb(s2[0]) // replace the array item with whatever
: interpolator.join('') // nothing was between the interpolation pattern
}
return s2.join('') // merge splited array (part2)
}).join('') // merge everything
}input{
padding:5px;
width: 100%;
box-sizing: border-box;
margin-bottom: 20px;
}
*{
font: 14px Arial;
padding:5px;
}<input value="Everything between {{}} is {{processed}}" />
<div></div>来源：https://stackoverflow.com/questions/24850819/how-to-do-string-interpolation-in-javascript