String.prototype.substring()

Baseline

20157

substring() String

const str = "Mozilla";

console.log(str.substring(1, 3));
// : "oz"

console.log(str.substring(2));
// : "zilla"

substring(indexStart)
substring(indexStart, indexEnd)

indexStart
indexEnd

substring() indexStart indexEnd

indexEnd undefined substring()
indexStart indexEnd substring()
indexStart indexEnd substring() 2

0 stringName.length 0 stringName.length

NaN 0

substring()

substring() "Mozilla"

const anyString = "Mozilla";

console.log(anyString.substring(0, 1)); // "M"
console.log(anyString.substring(1, 0)); // "M"

console.log(anyString.substring(0, 6)); // "Mozill"

console.log(anyString.substring(4)); // "lla"
console.log(anyString.substring(4, 7)); // "lla"
console.log(anyString.substring(7, 4)); // "lla"

console.log(anyString.substring(0, 7)); // "Mozilla"
console.log(anyString.substring(0, 10)); // "Mozilla"

substring() length

substring() length

const text = "Mozilla";

//  4 
console.log(text.substring(text.length - 4)); // "illa" 

//  5 
console.log(text.substring(text.length - 5)); // "zilla"

substring() substr()

substring() substr()

substr() 2 start length substring() start end
substr() start substring() 0
substr() 0 substring() end start 2

substr() ECMAScript

const text = "Mozilla";
console.log(text.substring(2, 5)); // "zil"
console.log(text.substr(2, 3)); // "zil"

substring() slice()

substring() slice()

substring() indexStart indexEnd 2 slice()

const text = "Mozilla";
console.log(text.substring(5, 2)); // "zil"
console.log(text.slice(5, 2)); // ""

NaN substring() 0

console.log(text.substring(-5, 2)); // "Mo"
console.log(text.substring(-5, -2)); // ""

slice() NaN 0

console.log(text.slice(-5, 2)); // ""
console.log(text.slice(-5, -2)); // "zil"

slice()

Brave New World Brave New Web

// fullS  oldS  newS 
function replaceString(oldS, newS, fullS) {
  for (let i = 0; i < fullS.length; ++i) {
    if (fullS.substring(i, i + oldS.length) === oldS) {
      fullS =
        fullS.substring(0, i) +
        newS +
        fullS.substring(i + oldS.length, fullS.length);
    }
  }
  return fullS;
}

replaceString("World", "Web", "Brave New World");

oldS newS "World" "OtherWorld"

function replaceString(oldS, newS, fullS) {
  return fullS.split(oldS).join(newS);
}

substring String.prototype.replace()


ECMAScript 2027 LanguageSpecification # sec-string.prototype.substring

MDN

MDN 2025822

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