The ornamental design for a hairextension, as shown and described.
FIG. 1 is a perspective view of a hair extension according to the present invention;
FIG. 2 is a front view of the hair extension of FIG. 1;
FIG. 3 is a rear view of the hair extension of FIG. 1;
FIG. 4 is a left side view of the hair extension of FIG. 1;
FIG. 5 is a right side view of the hair extension of FIG. 1;
FIG. 6 is a top vie of the hair extension of FIG. 1;
FIG. 7 is a bottom view of the hair extension of FIG. 1;
FIG. 8 is an enlarged view of ‘A’ part of FIG. 1 and shows a composition of a cross-shaped hook part of the hair extension of the present invention; and,
FIG. 9 is a view showing development status of a fixed part prior to fixing the hair extension of the present invention.