"The Necklace" does not seem like the kind of story that would use foreshadowing, since anything of that nature would tend to detract from the truly shocking effect of the surprise ending. The Loisels and the reader are led to believe that the borrowed necklace is made of genuine diamonds. When Mme. Loisel first sees the necklace, Maupassant calls it "a superb diamond necklace." He is intentionally deceiving the reader here, but it is hard to see how he could do otherwise. He could hardly call it "what appeared to be a superb diamond necklace."
The only hint that the diamonds are fake can be detected in Mme. Forestier's reply to Mme. Loisel when she asks:
"Will you lend me this, only this?"
It would appear to the reader that she is asking to borrow the most expensive piece of jewelry in the whole collection. A necklace like that would cost at least $150,000 in present-day American dollars, possibly much more. Yet Mme. Forestier's reply might make an especially keen reader wonder. She replies:
"Why, yes, certainly."
The word "certainly" makes her reply seem to be expressing relief that she does not have to risk lending a truly valuable piece of jewelry, and also expressing relief that her friend says, "only this?"--meaning that she will not be asked to lend her several valuable items. Mme. Forestier knows the necklace is only worth about 500 francs. The word "certainly" also sounds a bit ironic. Mme. Forestier is somewhat amused by the fact that her friend thinks she is getting a fabulously expensive diamond necklace. It is as if Mme. Forestier is saying, "Why, yes," and then to herself, "if you're naive enough to think you're getting a real diamond necklace. The word "certainly" has many implications in this line of dialogue.
The fact that poor Mathilde Loisel actually believes she is wearing an exquisite diamond necklace at the ball enhances her enjoyment of the affair because it makes her feel even more beautiful than she is. This feeling shows in her face and in her posture, making her appear more alluring to all the men--most of whom, except for a sophisticated few, probably think the necklace is real too.
Maupassant's story depends heavily on the surprise ending. He not only does not hint that Mme. Loisel will find out she has ruined her life over a fake necklace, but he deliberately misleads the reader by calling the piece of fake jewelry "a superb diamond necklace." This might be described as the opposite of foreshadowing. (It might also be called "cheating.")