How to convert a string to a boolean in JavaScript

  • August 31, 2026
  • 3-minute read
  • Last updated: August 31, 2026

The reason this question has 111 answers is one line:

Boolean("false") = true

Every non-empty string is true

Boolean("true"     ) = true
Boolean("false"    ) = true
Boolean("0"        ) = true
Boolean(""         ) = false
Boolean(" "        ) = true
Boolean("null"     ) = true

Boolean() is not a parser. It asks whether the value is truthy, and every string except "" is. "false", "0" and even a single space all come back true.

The two other spellings behave the same, because they are the same thing:

!!"false"      : true
if ("false")   : taken

Comparing to the string

cmp("true") = true   cmp("TRUE") = false   cmp("1") = false

s === "true" is the accepted answer and it is correct as far as it goes. Note what it decides for you: "TRUE" is false, and so is "1". If your input comes from a config file or a checkbox, that may well be wrong.

One toLowerCase() and a trim() fix the obvious part:

cmp2(" True ") = true

JSON.parse, and why not

JSON.parse("true" ) = true  (boolean)
JSON.parse("1"    ) = 1  (number)
JSON.parse("yes"  ) throws: SyntaxError: Unexpected token 'y', "yes" is not valid JSON
JSON.parse(""     ) throws: SyntaxError: Unexpected end of JSON input
JSON.parse("TRUE" ) throws: SyntaxError: Unexpected token 'T', "TRUE" is not valid JSON

Two problems. JSON.parse returns the number 1 for "1", not a boolean — so typeof lies to whatever comes next. And it throws on anything that is not JSON, including the empty string, which is a realistic value for a missing form field.

Where these strings come from

a="true"   Boolean=true  ==="true"=true
b="false"  Boolean=true  ==="true"=false
c="0"      Boolean=true  ==="true"=false
d=""       Boolean=false ==="true"=false

That is a ?a=true&b=false&c=0&d= query string read back with URLSearchParams. A URL has no types. ?b=false arrives as the string "false", which is truthy, which means the opposite of what the person writing the URL intended.

localStorage does the same thing: store false, read back "false". Same for a data- attribute, a .env file and most database drivers’ TEXT columns.

Non-strings arrive too

[]   Boolean=true  ==="true"=false ==true=false
{}   Boolean=true  ==="true"=false ==true=false
"0"  Boolean=true  ==="true"=false ==true=false

[] == true is false while Boolean([]) is true. Whatever intuition you have about ==, it does not survive contact with this table — don’t use it here.

A converter that decides

const toBool = (v, dflt = false) => {
  if (typeof v === "boolean") return v;
  const s = String(v).trim().toLowerCase();
  if (["true", "1", "yes", "on"].includes(s)) return true;
  if (["false", "0", "no", "off", ""].includes(s)) return false;
  return dflt;
};

toBool("true")=true   toBool("TRUE")=true   toBool(" on ")=true   toBool("1")=true
toBool("false")=false toBool("0")=false     toBool("no")=false    toBool("")=false
toBool("banana")=false  toBool(true)=true   toBool(null)=false

The last row is the point. "banana" is not a boolean, and something has to happen — a default you chose and can see, rather than true because the string happened to be non-empty.

Which strings belong in each list is your decision, not JavaScript’s. Write it down where the next person can read it.

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