feat: add an n specifier that prints nothing

README.md

@@ -69,6 +69,7 @@ The placeholders in the format string are marked by `%` and are followed by one
     * `u` — yields an integer as an unsigned decimal number
     * `f` — yields a float as is; see notes on precision above
     * `g` — yields a float as is; see notes on precision above
+    * `n` — yields nothing
     * `o` — yields an integer as an octal number
     * `s` — yields a string as is
     * `t` — yields `true` or `false`

src/sprintf.js

@@ -8,13 +8,14 @@
         not_bool: /[^t]/,
         not_type: /[^T]/,
         not_primitive: /[^v]/,
+        nothing: /[n]/,
         number: /[diefg]/,
         numeric_arg: /[bcdiefguxX]/,
         json: /[j]/,
         not_json: /[^j]/,
         text: /^[^\x25]+/,
         modulo: /^\x25{2}/,
-        placeholder: /^\x25(?:([1-9]\d*)\$|\(([^)]+)\))?(\+)?(0|'[^$])?(-)?(\d+)?(?:\.(\d+))?([b-gijostTuvxX])/,
+        placeholder: /^\x25(?:([1-9]\d*)\$|\(([^)]+)\))?(\+)?(0|'[^$])?(-)?(\d+)?(?:\.(\d+))?([b-gijnostTuvxX])/,
         key: /^([a-z_][a-z_\d]*)/i,
         key_access: /^\.([a-z_][a-z_\d]*)/i,
         index_access: /^\[(\d+)\]/,
@@ -89,6 +90,9 @@
                     case 'g':
                         arg = ph.precision ? String(Number(arg.toPrecision(ph.precision))) : parseFloat(arg)
                         break
+                    case 'n':
+                        arg = ''
+                        break
                     case 'o':
                         arg = (parseInt(arg, 10) >>> 0).toString(8)
                         break
@@ -118,7 +122,10 @@
                         arg = (parseInt(arg, 10) >>> 0).toString(16).toUpperCase()
                         break
                 }
-                if (re.json.test(ph.type)) {
+                if (re.nothing.test(ph.type)) {
+                    output += arg
+                }
+                else if (re.json.test(ph.type)) {
                     output += arg
                 }
                 else {

test/test.js

@@ -58,6 +58,10 @@ describe('sprintfjs', function() {
         assert.equal('1,2,3', sprintf('%v', [1, 2, 3]))
         assert.equal('[object Object]', sprintf('%v', {foo: 'bar'}))
         assert.equal('/<("[^"]*"|\'[^\']*\'|[^\'">])*>/', sprintf('%v', /<("[^"]*"|'[^']*'|[^'">])*>/))
+
+        assert.equal('', sprintf('%n', 42))
+        assert.equal('', sprintf('%2$n', 'foo', 'bar', 'baz'))
+        assert.equal('Hello !', sprintf('Hello %(name)n!', {name: 'world'}))
     })
 
     it('should return formated strings for complex placeholders', function() {
@@ -104,6 +108,9 @@ describe('sprintfjs', function() {
         assert.equal('xxxxx', sprintf('%5.5s', 'xxxxxx'))
         assert.equal('    x', sprintf('%5.1s', 'xxxxxx'))
 
+        // mixed nothing
+        assert.equal('', sprintf("%+'#10n", -123))
+        assert.equal('foobaz', sprintf('%s%n%s', 'foo', 'bar', 'baz'))
     })
 
     it('should return formated strings for callbacks', function() {