How to use 'javascript concatenate string and variable' in JavaScript

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concatenateString(binaryExpression, string = '') {
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  if (binaryExpression.operatorToken.kind !== ts.SyntaxKind.PlusToken) {
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    return
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  }
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  if (binaryExpression.left.kind === ts.SyntaxKind.BinaryExpression) {
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    string += this.concatenateString(binaryExpression.left, string)
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  }
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  else if (binaryExpression.left.kind === ts.SyntaxKind.StringLiteral) {
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    string += binaryExpression.left.text
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  }
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  else {
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    return
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  }
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  if (binaryExpression.right.kind === ts.SyntaxKind.BinaryExpression) {
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    string += this.concatenateString(binaryExpression.right, string)
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  }
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  else if (binaryExpression.right.kind === ts.SyntaxKind.StringLiteral) {
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    string += binaryExpression.right.text
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  }
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  else {
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    return
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  }
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  return string
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}

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function JS_STRING_CONCAT(a, b) {
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  return a + b;
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}